Expression

java.lang.Object
- net.sf.saxon.expr.Expression

All Implemented Interfaces:

IdentityComparable

Direct Known Subclasses:

ArrayBlock, Assignation, AxisExpression, BasicUpdatingExpression, BinaryExpression, CompiledExpression, ConditionalSorter, ContextItemExpression, CopyModifyExpression, CurrentGroupCall, CurrentGroupingKeyCall, ErrorExpression, EvaluateInstr, FLWORExpression, FunctionCall, IndexedLookupExpression, Instruction, IntegerRangeTest, IsLastExpression, Literal, NumberInstruction, PartialApply, PseudoExpression, RootExpression, SimpleExpression, SortExpression, SuppliedParameterReference, SwitchExpression, TryCatch, TupleExpression, UnaryExpression, UserFunctionReference, VariableReference, WhichOf
```
public abstract class Expression
extends Object
implements IdentityComparable
```
Interface supported by an XPath expression. This includes both compile-time and run-time methods.
Two expressions are considered equal if they return the same result when evaluated in the same context.

Expressions manage their own subexpressions but must observe certain conventions when doing so. Every expression must implement the methods operands() and getOperand(N) to access the operands of the expression; here N is an integer identifier for the subexpression which is unique among the subexpressions and whose allocation is a matter for each expression to determined. So a subexpression of an expression can change (during optimization rewrite, for example), then (a) the expression must implement the method setOperandExpression(N, expr) to effect the change, and (b) calling this method must cause a call on adoptChildExpression(N, expr) which is implemented in the expression class itself, and takes responsibility for maintaining the consistency of the tree, e.g. by invalidating cached information.

The default implementations of methods such as operands() work for expressions that have no subexpressions.

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`EFFECTIVE_BOOLEAN_VALUE`
`static int`	`EVALUATE_METHOD`
`static int`	`ITEM_FEED_METHOD`
`static int`	`ITERATE_METHOD`
`static IntegerValue`	`MAX_SEQUENCE_LENGTH`
`static IntegerValue`	`MAX_STRING_LENGTH`
`static int`	`PROCESS_METHOD`
`protected int`	`staticProperties`
`static IntegerValue`	`UNBOUNDED_LOWER`
`static IntegerValue`	`UNBOUNDED_UPPER`
`static int`	`UPDATE_METHOD`
`static int`	`WATCH_METHOD`

Constructor Summary

Constructors
Constructor and Description

Expression()

Constructors
Constructor and Description
`Expression()`

Method Summary

Methods
Modifier and Type	Method and Description
`PathMap.PathMapNodeSet`	`addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)` Add a representation of this expression to a PathMap.
`void`	`adoptChildExpression(Expression child)` Set up a parent-child relationship between this expression and a given child expression.
`Iterable<Operand>`	`checkedOperands()` Get the immediate sub-expressions of this expression, verifying that the parent pointers in the child expressions are correct.
`void`	`checkForUpdatingSubexpressions()` Check to ensure that this expression does not contain any inappropriate updating subexpressions.
`void`	`checkPermittedContents(SchemaType parentType, boolean whole)` Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
`void`	`clearStreamabilityData()`
`protected abstract int`	`computeCardinality()` Compute the static cardinality of this expression
`int`	`computeDependencies()` Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.
`protected int`	`computeSpecialProperties()` Compute the special properties of this expression.
`void`	`computeStaticProperties()` Compute the static properties.
`abstract Expression`	`copy()` Copy an expression.
`Expression`	`doPromotion(Expression subexpression, PromotionOffer offer)` Promote a subexpression if possible, and if the expression was changed, carry out housekeeping to reset the static properties and correct the parent pointers in the tree
`protected void`	`dynamicError(String message, String code, XPathContext context)` Method used in subclasses to signal a dynamic error
`boolean`	`effectiveBooleanValue(XPathContext context)` Get the effective boolean value of the expression.
`CharSequence`	`evaluateAsString(XPathContext context)` Evaluate an expression as a String.
`Item`	`evaluateItem(XPathContext context)` Evaluate an expression as a single item.
`void`	`evaluatePendingUpdates(XPathContext context, PendingUpdateList pul)` Evaluate an updating expression, adding the results to a Pending Update List.
`void`	`explain(Logger out)` Diagnostic print of expression structure.
`abstract void`	`export(ExpressionPresenter out)` Diagnostic print of expression structure.
`int`	`getCardinality()` Determine the static cardinality of the expression.
`Configuration`	`getConfiguration()` Get the configuration containing this expression
`int`	`getConstructType()` Get the type of this expression for use in tracing and diagnostics
`int`	`getCost()` Return the estimated cost of evaluating an expression.
`int`	`getDependencies()` Determine which aspects of the context the expression depends on.
`int`	`getEvaluationMethod()`
`ExpressionCompiler`	`getExpressionCompiler()` Return the compiler relating to a particular expression
`String`	`getExpressionName()` Get a name identifying the kind of expression, in terms meaningful to a user.
`int`	`getHostLanguage()` Get the host language (XSLT, XQuery, XPath) used to implement the code in this container
`abstract int`	`getImplementationMethod()` An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
`IntegerValue[]`	`getIntegerBounds()` For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.
`int`	`getIntrinsicDependencies()` Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
`abstract ItemType`	`getItemType()` Determine the data type of the expression, if possible.
`Location`	`getLocation()` Get the location of the expression
`protected int`	`getNetCost()` Return the net cost of evaluating this expression, excluding the cost of evaluating its operands.
`StructuredQName`	`getObjectName()`
`PackageData`	`getPackageData()` Get information about the containing package
`Expression`	`getParentExpression()` Get the parent expression of this expression in the expression tree.
`Posture`	`getPosture()`
`PostureAndSweep`	`getPostureAndSweepIfKnown()` Get the posture and sweep of the expression if these have already been computed
`Iterator<String>`	`getProperties()` Get an iterator over all the properties available.
`Object`	`getProperty(String name)`
`RetainedStaticContext`	`getRetainedStaticContext()` Get the retained static context of the expression
`int[]`	`getSlotsUsed()` Get the local variables (identified by their slot numbers) on which this expression depends.
`int`	`getSpecialProperties()` Get the static properties of this expression (other than its type).
`URI`	`getStaticBaseURI()` Get the saved static base URI as a URI
`String`	`getStaticBaseURIString()` Get the saved static base URI as a string
`PostureAndSweep`	`getStreamability(boolean allowExtensions, ContextItemStaticInfo contextInfo, List<String> reasons)` Get the posture and sweep of this expression as defined in the W3C streamability specifications.
`protected StreamingAdjunct`	`getStreamingAdjunct()` Get an object that supports streamed evaluation of this expression
`Sweep`	`getSweep()`
`String`	`getSystemId()`
`boolean`	`hasVariableBinding(Binding binding)` Ask whether this expression is, or contains, the binding of a given variable
`int`	`identityHashCode()` Get a hashCode that offers the guarantee that if A.isIdentical(B), then A.identityHashCode() == B.identityHashCode()
`boolean`	`implementsStaticTypeCheck()` Determine whether this expression implements its own method for static type checking
`boolean`	`isCallOn(Class<? extends SystemFunction> function)` Ask whether this expression is a call on a particular function
`boolean`	`isCallOnSystemFunction(String localName)`
`boolean`	`isIdentical(IdentityComparable other)` Determine whether two IdentityComparable objects are identical.
`boolean`	`isSubtreeExpression()` Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
`boolean`	`isUpdatingExpression()` Determine whether this is an updating expression as defined in the XQuery update specification
`boolean`	`isVacuousExpression()` Determine whether this is a vacuous expression as defined in the XQuery update specification
`SequenceIterator`	`iterate(XPathContext context)` Return an Iterator to iterate over the values of a sequence.
`EventIterator`	`iterateEvents(XPathContext context)` Deliver the result of the expression as a sequence of events.
`static StreamingAdjunct`	`makeStreamingAdjunct(Configuration config, Expression exp)` Make a streaming adjunct for a particular expression.
`int`	`markTailFunctionCalls(StructuredQName qName, int arity)` Mark tail-recursive calls on stylesheet functions.
`protected List<Operand>`	`operandList(Operand... a)` Helper method for subclasses to build a list of operands
`Iterable<Operand>`	`operands()` Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
`protected List<Operand>`	`operandSparseList(Operand... a)` Helper method for subclasses to build a list of operands
`Expression`	`optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` Perform optimisation of an expression and its subexpressions.
`protected void`	`optimizeChildren(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` Perform optimization of the children of this expression (and their children, recursively) This method is provided as a helper for implementations of the `optimize(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo)` method, since optimizing the children is an inevitable part of optimizing the expression itself
`Expression`	`optimizeForType(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)`
`void`	`process(XPathContext context)` Process the instruction, without returning any tail calls
`Expression`	`promote(PromotionOffer offer)` Offer promotion for this subexpression.
`protected void`	`promoteChildren(PromotionOffer offer)` Helper method for implementations of `promote(net.sf.saxon.expr.parser.PromotionOffer)` to apply the requested promotion to all subexpressions
`void`	`resetLocalStaticProperties()` Reset the static properties of the expression to -1, so that they have to be recomputed next time they are used.
`void`	`restoreParentPointers()` Restore parent pointers for the subtree rooted at this expression
`void`	`setEvaluationMethod(int method)`
`void`	`setFiltered(boolean filtered)` Mark an expression as filtered: that is, it appears as the base expression in a filter expression.
`void`	`setFlattened(boolean flattened)` Mark an expression as being "flattened".
`void`	`setLocation(Location id)` Set the location on an expression.
`void`	`setParentExpression(Expression parent)` Set the parent expression of this expression in the expression tree.
`void`	`setPostureAndSweep(PostureAndSweep ps)`
`void`	`setRetainedStaticContext(RetainedStaticContext rsc)` Set the retained static context
`void`	`setRetainedStaticContextLocally(RetainedStaticContext rsc)` Set the parts of the static context that might be needed by the function, without passing them on to subexpressions.
`void`	`setStaticProperty(int prop)` Set a static property on an expression.
`Expression`	`simplify()` Simplify an expression.
`protected void`	`simplifyChildren()` Simplify an expression.
`Expression`	`staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleDiagnostic role, ExpressionVisitor visitor)` Static type checking of some expressions is delegated to the expression itself, by calling this method.
`void`	`suppressValidation(int parentValidationMode)` Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation.
`Pattern`	`toPattern(Configuration config, boolean is30)` Convert this expression to an equivalent XSLT pattern
`String`	`toShortString()` Produce a short string identifying the expression for use in error messages
`Pattern`	`toStreamingPattern(Configuration config)` Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)
`String`	`toString()` The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
`Expression`	`typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` Perform type checking of an expression and its subexpressions.
`protected void`	`typeCheckChildren(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` Perform type checking of the children of this expression (and their children, recursively) This method is provided as a helper for implementations of the `typeCheck(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo)` method, since checking the children is an inevitable part of checking the expression itse.f
`protected void`	`typeError(String message, String errorCode, XPathContext context)` Method used in subclasses to signal a runtime type error
`Expression`	`unordered(boolean retainAllNodes, boolean forStreaming)` Replace this expression by a simpler expression that delivers the results without regard to order.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - EVALUATE_METHOD
```
public static final int EVALUATE_METHOD
```
    See Also:
    Constant Field Values
  - ITERATE_METHOD
```
public static final int ITERATE_METHOD
```
    See Also:
    Constant Field Values
  - PROCESS_METHOD
```
public static final int PROCESS_METHOD
```
    See Also:
    Constant Field Values
  - WATCH_METHOD
```
public static final int WATCH_METHOD
```
    See Also:
    Constant Field Values
  - ITEM_FEED_METHOD
```
public static final int ITEM_FEED_METHOD
```
    See Also:
    Constant Field Values
  - EFFECTIVE_BOOLEAN_VALUE
```
public static final int EFFECTIVE_BOOLEAN_VALUE
```
    See Also:
    Constant Field Values
  - UPDATE_METHOD
```
public static final int UPDATE_METHOD
```
    See Also:
    Constant Field Values
  - staticProperties
```
protected int staticProperties
```
  - UNBOUNDED_LOWER
```
public static final IntegerValue UNBOUNDED_LOWER
```
  - UNBOUNDED_UPPER
```
public static final IntegerValue UNBOUNDED_UPPER
```
  - MAX_STRING_LENGTH
```
public static final IntegerValue MAX_STRING_LENGTH
```
  - MAX_SEQUENCE_LENGTH
```
public static final IntegerValue MAX_SEQUENCE_LENGTH
```
- Constructor Detail
  - Expression
```
public Expression()
```
- Method Detail
  - getExpressionName
```
public String getExpressionName()
```
    Get a name identifying the kind of expression, in terms meaningful to a user.
    
    Returns:
    a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.
  - operands
```
public Iterable<Operand> operands()
```
    Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()
    If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.
    
    Returns:
    an iterator containing the sub-expressions of this expression
  - checkedOperands
```
public final Iterable<Operand> checkedOperands()
```
    Get the immediate sub-expressions of this expression, verifying that the parent pointers in the child expressions are correct.
    
    Returns:
    the list of sub-expressions, in the same way as with the operands() method, but with additional checking
  - operandList
```
protected List<Operand> operandList(Operand... a)
```
    Helper method for subclasses to build a list of operands
    
    Parameters:
    a - the sequence of operands (which must all be non-null)
    
    Returns:
    a list of operands
  - operandSparseList
```
protected List<Operand> operandSparseList(Operand... a)
```
    Helper method for subclasses to build a list of operands
    
    Parameters:
    a - the sequence of operands; any null values in the list are ignored
    
    Returns:
    a list of operands
  - getParentExpression
```
public Expression getParentExpression()
```
    Get the parent expression of this expression in the expression tree.
    
    Returns:
    the parent expression. Null if at the root of the tree, for example, the expression representing the body of a function or template.
  - getSystemId
```
public String getSystemId()
```
  - setParentExpression
```
public void setParentExpression(Expression parent)
```
    Set the parent expression of this expression in the expression tree.
    
    Parameters:
    parent - the parent expression
  - restoreParentPointers
```
public void restoreParentPointers()
```
    Restore parent pointers for the subtree rooted at this expression
  - getImplementationMethod
```
public abstract int getImplementationMethod()
```
    An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.
    
    Returns:
    the implementation method, for example ITERATE_METHOD or EVALUATE_METHOD or PROCESS_METHOD
  - implementsStaticTypeCheck
```
public boolean implementsStaticTypeCheck()
```
    Determine whether this expression implements its own method for static type checking
    
    Returns:
    true if this expression has a non-trivial implementation of the staticTypeCheck() method
  - hasVariableBinding
```
public boolean hasVariableBinding(Binding binding)
```
    Ask whether this expression is, or contains, the binding of a given variable
    
    Parameters:
    binding - the variable binding
    
    Returns:
    true if this expression is the variable binding (for example a ForExpression or LetExpression) or if it is a FLWOR expression that binds the variable in one of its clauses.
  - simplify
```
public Expression simplify()
                    throws XPathException
```
    Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation simplifies its operands.
    
    Returns:
    the simplified expression (or the original if unchanged, or if modified in-situ)
    
    Throws:
    
    XPathException - if an error is discovered during expression rewriting
  - simplifyChildren
```
protected final void simplifyChildren()
                               throws XPathException
```
    Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation simplifies its operands.
    
    Throws:
    
    XPathException - if an error is discovered during expression rewriting
  - setRetainedStaticContext
```
public void setRetainedStaticContext(RetainedStaticContext rsc)
```
    Set the retained static context
    
    Parameters:
    rsc - the static context to be retained
  - setRetainedStaticContextLocally
```
public void setRetainedStaticContextLocally(RetainedStaticContext rsc)
```
    Set the parts of the static context that might be needed by the function, without passing them on to subexpressions. Used for dynamic function calls only.
  - getRetainedStaticContext
```
public final RetainedStaticContext getRetainedStaticContext()
```
    Get the retained static context of the expression
    
    Returns:
    the retained static context
  - getStaticBaseURIString
```
public String getStaticBaseURIString()
```
    Get the saved static base URI as a string
    
    Returns:
    the static base URI
  - getStaticBaseURI
```
public URI getStaticBaseURI()
                     throws XPathException
```
    Get the saved static base URI as a URI
    
    Returns:
    the static base URI as a URI
    
    Throws:
    
    XPathException
  - isCallOn
```
public boolean isCallOn(Class<? extends SystemFunction> function)
```
    Ask whether this expression is a call on a particular function
    
    Parameters:
    function - the implementation class of the function in question
  - isCallOnSystemFunction
```
public boolean isCallOnSystemFunction(String localName)
```
  - typeCheck
```
public Expression typeCheck(ExpressionVisitor visitor,
                   ContextItemStaticInfo contextInfo)
                     throws XPathException
```
    Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.
    
    This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.
    
    This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.
    
    Parameters:
    visitor - an expression visitor
    contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
    
    Returns:
    the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
    
    Throws:
    
    XPathException - if an error is discovered during this phase (typically a type error)
  - typeCheckChildren
```
protected final void typeCheckChildren(ExpressionVisitor visitor,
                     ContextItemStaticInfo contextInfo)
                                throws XPathException
```
    Perform type checking of the children of this expression (and their children, recursively) This method is provided as a helper for implementations of the typeCheck(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo) method, since checking the children is an inevitable part of checking the expression itse.f
    
    Parameters:
    visitor - an expression visitor
    contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
    
    Throws:
    
    XPathException - if an error is discovered during this phase (typically a type error)
  - staticTypeCheck
```
public Expression staticTypeCheck(SequenceType req,
                         boolean backwardsCompatible,
                         RoleDiagnostic role,
                         ExpressionVisitor visitor)
                           throws XPathException
```
    Static type checking of some expressions is delegated to the expression itself, by calling this method. The default implementation of the method throws UnsupportedOperationException. If there is a non-default implementation, then implementsStaticTypeCheck() will return true
    
    Parameters:
    req - the required type
    backwardsCompatible - true if backwards compatibility mode applies
    role - the role of the expression in relation to the required type
    visitor - an expression visitor
    
    Returns:
    the expression after type checking (perhaps augmented with dynamic type checking code)
    
    Throws:
    
    XPathException - if failures occur, for example if the static type of one branch of the conditional is incompatible with the required type
  - optimize
```
public Expression optimize(ExpressionVisitor visitor,
                  ContextItemStaticInfo contextInfo)
                    throws XPathException
```
    Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.
    
    This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.
    
    Parameters:
    visitor - an expression visitor
    contextInfo - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
    
    Returns:
    the original expression, rewritten if appropriate to optimize execution
    
    Throws:
    
    XPathException - if an error is discovered during this phase (typically a type error)
  - optimizeChildren
```
protected final void optimizeChildren(ExpressionVisitor visitor,
                    ContextItemStaticInfo contextInfo)
                               throws XPathException
```
    Perform optimization of the children of this expression (and their children, recursively) This method is provided as a helper for implementations of the optimize(net.sf.saxon.expr.parser.ExpressionVisitor, net.sf.saxon.expr.parser.ContextItemStaticInfo) method, since optimizing the children is an inevitable part of optimizing the expression itself
    
    Parameters:
    visitor - an expression visitor
    contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
    
    Throws:
    
    XPathException - if an error is discovered during this phase (typically a type error)
  - getCost
```
public int getCost()
```
    Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.
    
    Returns:
    an estimate of the gross cost of evaluating the expression, including the cost of evaluating its operands.
  - getNetCost
```
protected int getNetCost()
```
    Return the net cost of evaluating this expression, excluding the cost of evaluating its operands. We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one).
    
    Returns:
    the intrinsic cost of this operation, excluding the costs of evaluating the operands
  - promote
```
public Expression promote(PromotionOffer offer)
                   throws XPathException
```
    Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is accepted. This method is always called at compile time.
    
    Parameters:
    offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
    
    Returns:
    if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
    
    Throws:
    
    XPathException - if any error is detected
  - promoteChildren
```
protected void promoteChildren(PromotionOffer offer)
                        throws XPathException
```
    Helper method for implementations of promote(net.sf.saxon.expr.parser.PromotionOffer) to apply the requested promotion to all subexpressions
    
    Parameters:
    offer - the promotion offer
    
    Throws:
    
    XPathException - if any failure occurs
  - doPromotion
```
public final Expression doPromotion(Expression subexpression,
                     PromotionOffer offer)
                             throws XPathException
```
    Promote a subexpression if possible, and if the expression was changed, carry out housekeeping to reset the static properties and correct the parent pointers in the tree
    
    Parameters:
    subexpression - the subexpression that is a candidate for promotion
    offer - details of the promotion being considered @return the result of the promotion. This will be the current expression if no promotion actions have taken place
    
    Returns:
    the expression that results from doing the promotion as requested. Returns null if and only if the supplied subexpression is null.
    
    Throws:
    
    XPathException - if an error occurs
  - unordered
```
public Expression unordered(boolean retainAllNodes,
                   boolean forStreaming)
                     throws XPathException
```
    Replace this expression by a simpler expression that delivers the results without regard to order.
    
    Parameters:
    retainAllNodes - set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.
    forStreaming - set to true if the result is to be optimized for streaming
    
    Returns:
    an expression that delivers the same nodes in a more convenient order
    
    Throws:
    
    XPathException - if the rewrite fails
  - getSpecialProperties
```
public final int getSpecialProperties()
```
    Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
    
    Returns:
    a set of flags indicating static properties of this expression
  - getCardinality
```
public int getCardinality()
```
    Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.
    
    Returns:
    one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).
  - getItemType
```
public abstract ItemType getItemType()
```
    Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.
    
    This method should always return a result, though it may be the best approximation that is available at the time.
    
    Returns:
    a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
  - getDependencies
```
public int getDependencies()
```
    Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.
    
    Returns:
    a set of bit-significant flags identifying the dependencies of the expression
  - getIntegerBounds
```
public IntegerValue[] getIntegerBounds()
```
    For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
    
    Returns:
    the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.
  - setFlattened
```
public void setFlattened(boolean flattened)
```
    Mark an expression as being "flattened". This is a collective term that includes extracting the string value or typed value, or operations such as simple value construction that concatenate text nodes before atomizing. The implication of all of these is that although the expression might return nodes, the identity of the nodes has no significance. This is called during type checking of the parent expression.
    
    Parameters:
    flattened - set to true if the result of the expression is atomized or otherwise turned into an atomic value
  - setFiltered
```
public void setFiltered(boolean filtered)
```
    Mark an expression as filtered: that is, it appears as the base expression in a filter expression. This notification currently has no effect except when the expression is a variable reference.
    
    Parameters:
    filtered - if true, marks this expression as the base of a filter expression
  - evaluateItem
```
public Item evaluateItem(XPathContext context)
                  throws XPathException
```
    Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
    
    Parameters:
    context - The context in which the expression is to be evaluated
    
    Returns:
    the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
    
    Throws:
    
    XPathException - if any dynamic error occurs evaluating the expression
  - iterate
```
public SequenceIterator iterate(XPathContext context)
                         throws XPathException
```
    Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
    
    Parameters:
    context - supplies the context for evaluation
    
    Returns:
    a SequenceIterator that can be used to iterate over the result of the expression
    
    Throws:
    
    XPathException - if any dynamic error occurs evaluating the expression
  - iterateEvents
```
public EventIterator iterateEvents(XPathContext context)
                            throws XPathException
```
    Deliver the result of the expression as a sequence of events.
    
    The events (of class PullEvent) are either complete items, or one of startElement, endElement, startDocument, or endDocument, known as semi-nodes. The stream of events may also include a nested EventIterator. If a start-end pair exists in the sequence, then the events between this pair represent the content of the document or element. The content sequence will have been processed to the extent that any attribute and namespace nodes in the content sequence will have been merged into the startElement event. Namespace fixup will have been performed: that is, unique prefixes will have been allocated to element and attribute nodes, and all namespaces will be declared by means of a namespace node in the startElement event or in an outer startElement forming part of the sequence. However, duplicate namespaces may appear in the sequence.
    
    The content of an element or document may include adjacent or zero-length text nodes, atomic values, and nodes represented as nodes rather than broken down into events.
    
    Parameters:
    context - The dynamic evaluation context
    
    Returns:
    the result of the expression as an iterator over a sequence of PullEvent objects
    
    Throws:
    
    XPathException - if a dynamic error occurs during expression evaluation
  - effectiveBooleanValue
```
public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
```
    Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.
    
    Parameters:
    context - The context in which the expression is to be evaluated
    
    Returns:
    the effective boolean value
    
    Throws:
    
    XPathException - if any dynamic error occurs evaluating the expression
  - evaluateAsString
```
public CharSequence evaluateAsString(XPathContext context)
                              throws XPathException
```
    Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.
    
    Parameters:
    context - The context in which the expression is to be evaluated
    
    Returns:
    the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
    
    Throws:
    
    XPathException - if any dynamic error occurs evaluating the expression
    
    ClassCastException - if the result type of the expression is not xs:string?, xs:untypedAtomic?, or xs:anyURI?
  - process
```
public void process(XPathContext context)
             throws XPathException
```
    Process the instruction, without returning any tail calls
    
    Parameters:
    context - The dynamic context, giving access to the current node, the current variables, etc.
    
    Throws:
    
    XPathException - if a dynamic error occurs
  - evaluatePendingUpdates
```
public void evaluatePendingUpdates(XPathContext context,
                          PendingUpdateList pul)
                            throws XPathException
```
    Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException
    
    Parameters:
    context - the XPath dynamic evaluation context
    pul - the pending update list to which the results should be written
    
    Throws:
    
    XPathException - if evaluation fails
    
    UnsupportedOperationException - if the expression is not an updating expression
  - toString
```
public String toString()
```
    The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
    
    For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression. The expression produced should be equivalent to the original making certain assumptions about the static context. In general the expansion will make no assumptions about namespace bindings, except that (a) the prefix "xs" is used to refer to the XML Schema namespace, and (b) the default function namespace is assumed to be the "fn" namespace.
    
    In the case of XSLT instructions and XQuery expressions, the toString() method gives an abstracted view of the syntax that is not designed in general to be parseable.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    a representation of the expression as a string
  - toShortString
```
public String toShortString()
```
    Produce a short string identifying the expression for use in error messages
    
    Returns:
    a short string, sufficient to identify the expression
  - export
```
public abstract void export(ExpressionPresenter out)
```
    Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
    
    Parameters:
    out - the expression presenter used to display the structure
  - explain
```
public final void explain(Logger out)
```
    Diagnostic print of expression structure. The abstract expression tree is written to the supplied outputstream.
    
    Parameters:
    out - the expression presenter used to display the structure
  - checkPermittedContents
```
public void checkPermittedContents(SchemaType parentType,
                          boolean whole)
                            throws XPathException
```
    Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.
    
    Parameters:
    parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type
    whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content
    
    Throws:
    
    XPathException - if the value delivered by this expression cannot be part of the content model of the given type
  - adoptChildExpression
```
public void adoptChildExpression(Expression child)
```
    Set up a parent-child relationship between this expression and a given child expression.
    Note: many calls on this method are now redundant, but are kept in place for "belt-and-braces" reasons. The rule is that an implementation of simplify(), typeCheck(), or optimize() that returns a value other than "this" is required to set the location information and parent pointer in the new child expression. However, in the past this was often left to the caller, which did it by calling this method, either unconditionally on return from one of these methods, or after testing that the returned object was not the same as the original.
    
    Parameters:
    child - the child expression
  - setLocation
```
public void setLocation(Location id)
```
    Set the location on an expression.
    
    Parameters:
    id - the location
  - getLocation
```
public final Location getLocation()
```
    Get the location of the expression
    
    Returns:
    a location identifier, which can be turned into real location information by reference to a location provider
  - getConfiguration
```
public Configuration getConfiguration()
```
    Get the configuration containing this expression
    
    Returns:
    the containing Configuration
  - getPackageData
```
public PackageData getPackageData()
```
    Get information about the containing package
    
    Returns:
    package data
  - computeStaticProperties
```
public final void computeStaticProperties()
```
    Compute the static properties. This should only be done once for each expression.
  - resetLocalStaticProperties
```
public void resetLocalStaticProperties()
```
    Reset the static properties of the expression to -1, so that they have to be recomputed next time they are used.
  - computeCardinality
```
protected abstract int computeCardinality()
```
    Compute the static cardinality of this expression
    
    Returns:
    the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE
  - computeSpecialProperties
```
protected int computeSpecialProperties()
```
    Compute the special properties of this expression. These properties are denoted by a bit-significant integer, possible values are in class StaticProperty. The "special" properties are properties other than cardinality and dependencies, and most of them relate to properties of node sequences, for example whether the nodes are in document order.
    
    Returns:
    the special properties, as a bit-significant integer
  - computeDependencies
```
public int computeDependencies()
```
    Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.
    
    Returns:
    the depencies, as a bit-mask
  - getIntrinsicDependencies
```
public int getIntrinsicDependencies()
```
    Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".
    
    Returns:
    a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
  - setStaticProperty
```
public void setStaticProperty(int prop)
```
    Set a static property on an expression. Used when inlining functions to retain properties of the inlined function (though this is only partially successful because the properties can be recomputed later
    
    Parameters:
    prop - the property to be set
  - checkForUpdatingSubexpressions
```
public void checkForUpdatingSubexpressions()
                                    throws XPathException
```
    Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.
    
    Throws:
    
    XPathException - if the expression has a non-permitted updating subexpression
  - isUpdatingExpression
```
public boolean isUpdatingExpression()
```
    Determine whether this is an updating expression as defined in the XQuery update specification
    
    Returns:
    true if this is an updating expression
  - isVacuousExpression
```
public boolean isVacuousExpression()
```
    Determine whether this is a vacuous expression as defined in the XQuery update specification
    
    Returns:
    true if this expression is vacuous
  - copy
```
public abstract Expression copy()
```
    Copy an expression. This makes a deep copy.
    
    Returns:
    the copy of the original expression
  - suppressValidation
```
public void suppressValidation(int parentValidationMode)
```
    Suppress validation on contained element constructors, on the grounds that the parent element is already performing validation. The default implementation does nothing.
    
    Parameters:
    parentValidationMode - the kind of validation being performed on the parent expression
  - markTailFunctionCalls
```
public int markTailFunctionCalls(StructuredQName qName,
                        int arity)
```
    Mark tail-recursive calls on stylesheet functions. For most expressions, this does nothing.
    
    Parameters:
    qName - the name of the function
    arity - the arity (number of parameters) of the function
    
    Returns:
    UserFunctionCall.NOT_TAIL_CALL if no tail call was found; UserFunctionCall.FOREIGN_TAIL_CALL if a tail call on a different function was found;
  - toPattern
```
public Pattern toPattern(Configuration config,
                boolean is30)
                  throws XPathException
```
    Convert this expression to an equivalent XSLT pattern
    
    Parameters:
    config - the Saxon configuration
    is30 - true if this is XSLT 3.0
    
    Returns:
    the equivalent pattern
    
    Throws:
    
    XPathException - if conversion is not possible
  - toStreamingPattern
```
public Pattern toStreamingPattern(Configuration config)
```
    Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)
    
    Parameters:
    config - the Saxon configuration
    
    Returns:
    the equivalent pattern if conversion succeeds; otherwise null
  - getSlotsUsed
```
public final int[] getSlotsUsed()
```
    Get the local variables (identified by their slot numbers) on which this expression depends. Should only be called if the caller has established that there is a dependency on local variables.
    
    Returns:
    an array of integers giving the slot numbers of the local variables referenced in this expression.
  - dynamicError
```
protected void dynamicError(String message,
                String code,
                XPathContext context)
                     throws XPathException
```
    Method used in subclasses to signal a dynamic error
    
    Parameters:
    message - the error message
    code - the error code
    context - the XPath dynamic context
    
    Throws:
    
    XPathException - always thrown, to signal a dynamic error
  - typeError
```
protected void typeError(String message,
             String errorCode,
             XPathContext context)
                  throws XPathException
```
    Method used in subclasses to signal a runtime type error
    
    Parameters:
    message - the error message
    errorCode - the error code
    context - the XPath dynamic context
    
    Throws:
    
    XPathException - always thrown, to signal a dynamic error
  - getConstructType
```
public int getConstructType()
```
    Get the type of this expression for use in tracing and diagnostics
    
    Returns:
    the type of expression, as enumerated in class LocationKind
  - getObjectName
```
public StructuredQName getObjectName()
```
  - getProperty
```
public Object getProperty(String name)
```
  - getProperties
```
public Iterator<String> getProperties()
```
    Get an iterator over all the properties available. The values returned by the iterator will be of type String, and each string can be supplied as input to the getProperty() method to retrieve the value of the property. The iterator may return properties whose value is null.
  - getHostLanguage
```
public int getHostLanguage()
```
    Get the host language (XSLT, XQuery, XPath) used to implement the code in this container
    
    Returns:
    typically Configuration.XSLT or Configuration.XQUERY
  - addToPathMap
```
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                  PathMap.PathMapNodeSet pathMapNodeSet)
```
    Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
    
    The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.
    
    Parameters:
    pathMap - the PathMap to which the expression should be added
    pathMapNodeSet - the PathMapNodeSet to which the paths embodied in this expression should be added
    
    Returns:
    the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.
  - isSubtreeExpression
```
public boolean isSubtreeExpression()
```
    Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
    
    Returns:
    true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.
  - setEvaluationMethod
```
public void setEvaluationMethod(int method)
```
  - getEvaluationMethod
```
public int getEvaluationMethod()
```
  - isIdentical
```
public boolean isIdentical(IdentityComparable other)
```
    Determine whether two IdentityComparable objects are identical. This is a stronger test than equality (even schema-equality); for example two dateTime values are not identical unless they are in the same timezone. In the case of expressions, we test object identity, since the normal equality test ignores the location of the expression.
    
    Specified by:
    
    isIdentical in interface IdentityComparable
    
    Parameters:
    other - the value to be compared with
    
    Returns:
    true if the two values are indentical, false otherwise
  - identityHashCode
```
public int identityHashCode()
```
    Get a hashCode that offers the guarantee that if A.isIdentical(B), then A.identityHashCode() == B.identityHashCode()
    
    Specified by:
    
    identityHashCode in interface IdentityComparable
    
    Returns:
    a hashCode suitable for use when testing for identity.
  - getExpressionCompiler
```
public ExpressionCompiler getExpressionCompiler()
                                         throws CannotCompileException
```
    Return the compiler relating to a particular expression
    
    Returns:
    the relevant ExpressionCompiler
    
    Throws:
    
    CannotCompileException - if it is not possible to generate bytecode for this expression
  - makeStreamingAdjunct
```
public static StreamingAdjunct makeStreamingAdjunct(Configuration config,
                                    Expression exp)
```
    Make a streaming adjunct for a particular expression.
    
    Parameters:
    config - the Saxon Configuration
    exp - the expression to be compiled
    
    Returns:
    the compiler for this kind of expression
  - getStreamingAdjunct
```
protected StreamingAdjunct getStreamingAdjunct()
```
    Get an object that supports streamed evaluation of this expression
    
    Returns:
    the relevant StreamingAdjunct, or null if none is available
  - getStreamability
```
public final PostureAndSweep getStreamability(boolean allowExtensions,
                               ContextItemStaticInfo contextInfo,
                               List<String> reasons)
```
    Get the posture and sweep of this expression as defined in the W3C streamability specifications. This provides an assessment of stylesheet code against the W3C criteria for guaranteed streamability, and is implemented to allow these criteria to be tested. It is not the case that all expression that emerge as streamable from this analysis are currently capable of being streamed by Saxon
    
    Parameters:
    allowExtensions - if false, the definition of "guaranteed streamability" in the W3C specification is used. If true, Saxon extensions are permitted, which make some
    contextInfo - Information about the context item type and posture
    reasons - the caller may supply a list, in which case the implementation may add to this list a message explaining why the construct is not streamable, suitable for inclusion in an
    
    Returns:
    the posture and sweep of the expression
  - getPosture
```
public Posture getPosture()
```
  - getSweep
```
public Sweep getSweep()
```
  - getPostureAndSweepIfKnown
```
public PostureAndSweep getPostureAndSweepIfKnown()
```
    Get the posture and sweep of the expression if these have already been computed
    
    Returns:
    the posture and sweep if known, or null if the streamability has not yet been assessed.
  - clearStreamabilityData
```
public void clearStreamabilityData()
```
  - setPostureAndSweep
```
public void setPostureAndSweep(PostureAndSweep ps)
```
  - optimizeForType
```
public Expression optimizeForType(ExpressionVisitor visitor,
                         ContextItemStaticInfo contextItemType)
                           throws XPathException
```
    Throws:
    
    XPathException

Class Expression

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

EVALUATE_METHOD

ITERATE_METHOD

PROCESS_METHOD

WATCH_METHOD

ITEM_FEED_METHOD

EFFECTIVE_BOOLEAN_VALUE

UPDATE_METHOD

staticProperties

UNBOUNDED_LOWER

UNBOUNDED_UPPER

MAX_STRING_LENGTH

MAX_SEQUENCE_LENGTH

Constructor Detail

Expression

Method Detail

getExpressionName

operands

checkedOperands

operandList

operandSparseList

getParentExpression

getSystemId

setParentExpression

restoreParentPointers

getImplementationMethod

implementsStaticTypeCheck

hasVariableBinding

simplify

simplifyChildren

setRetainedStaticContext

setRetainedStaticContextLocally

getRetainedStaticContext

getStaticBaseURIString

getStaticBaseURI

isCallOn

isCallOnSystemFunction

typeCheck

typeCheckChildren

staticTypeCheck

optimize

optimizeChildren

getCost

getNetCost

promote

promoteChildren

doPromotion

unordered

getSpecialProperties

getCardinality

getItemType

getDependencies

getIntegerBounds

setFlattened

setFiltered

evaluateItem

iterate

iterateEvents

effectiveBooleanValue

evaluateAsString

process

evaluatePendingUpdates

toString

toShortString

export

explain

checkPermittedContents

adoptChildExpression

setLocation

getLocation

getConfiguration

getPackageData

computeStaticProperties

resetLocalStaticProperties

computeCardinality