net.sf.saxon.expr.instruct
Class Block

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.instruct.Instruction
          extended by net.sf.saxon.expr.instruct.Block
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, TailCallReturner, InstructionInfo, Locator

public class Block
extends Instruction

An expression that delivers the concatenation of the results of its subexpressions. This may represent an XSLT sequence constructor, or an XPath/XQuery expression of the form (a,b,c,d).

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
 
Constructor Summary
Block()
          Create an empty block
 
Method Summary
 void checkForUpdatingSubexpressions()
          Check to ensure that this expression does not contain any updating subexpressions.
 void checkPermittedContents(SchemaType parentType, StaticContext env, 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.
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 Expression copy()
          Copy an expression.
 boolean createsNewNodes()
          Determine whether this instruction creates new nodes.
 void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul)
          Evaluate an updating expression, adding the results to a Pending Update List.
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 int getCardinality()
          Determine the cardinality of the expression
 Expression[] getChildren()
          Get the children of this instruction
 String getExpressionName()
          Get a name identifying the kind of expression, in terms meaningful to a user.
 int getImplementationMethod()
          An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
 ItemType getItemType(TypeHierarchy th)
          Determine the data type of the items returned by this expression
 boolean isVacuousExpression()
          Determine whether this is a vacuous expression as defined in the XQuery update specification
 SequenceIterator<? extends Item> iterate(XPathContext context)
          Iterate over the results of all the child expressions
 EventIterator iterateEvents(XPathContext context)
          Get an EventIterator over the results of all the child expressions
 Iterator<Expression> iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
static Expression makeBlock(Expression e1, Expression e2)
          Static factory method to create a block.
static Expression makeBlock(List<Expression> list)
          Static factory method to create a block from a list of expressions
 Expression mergeAdjacentTextInstructions()
          Merge any adjacent instructions that create literal text nodes
 Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 TailCall processLeavingTail(XPathContext context)
          ProcessLeavingTail: called to do the real work of this instruction.
protected  void promoteInst(PromotionOffer offer)
          Handle promotion offers, that is, non-local tree rewrites.
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 void setChildren(Expression[] children)
          Set the children of this instruction
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression.
 Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
          Perform type checking of an expression and its subexpressions.
 
Methods inherited from class net.sf.saxon.expr.instruct.Instruction
assembleParams, assembleTunnelParams, computeCardinality, dynamicError, evaluateAsString, evaluateItem, getConstructType, getInstructionName, getInstructionNameCode, getIteratorFromProcessMethod, getSourceLocator, isXSLT, process, promote
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, explain, getColumnNumber, getColumnNumber, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, iterateSameFocusSubExpressions, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getLineNumber, getPublicId, getSystemId
 

Constructor Detail

Block

public Block()
Create an empty block

Method Detail

makeBlock

public static Expression makeBlock(Expression e1,
                                   Expression e2)
Static factory method to create a block. If one of the arguments is already a block, the contents will be merged into a new composite block

Parameters:
e1 - the first subexpression (child) of the block
e2 - the second subexpression (child) of the block
Returns:
a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

makeBlock

public static Expression makeBlock(List<Expression> list)
Static factory method to create a block from a list of expressions

Parameters:
list - the list of expressions making up this block. The members of the List must be instances of Expression
Returns:
a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence

setChildren

public void setChildren(Expression[] children)
Set the children of this instruction

Parameters:
children - The instructions that are children of this instruction

getExpressionName

public String getExpressionName()
Description copied from class: Instruction
Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:
getExpressionName in class Instruction
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 explain() output displaying the expression.

getChildren

public Expression[] getChildren()
Get the children of this instruction

Returns:
the children of this instruction, as an array of Instruction objects. May return a zero-length array if there are no children

computeSpecialProperties

public int computeSpecialProperties()
Description copied from class: Instruction
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.

Overrides:
computeSpecialProperties in class Instruction
Returns:
a set of flags indicating static properties of this expression

mergeAdjacentTextInstructions

public Expression mergeAdjacentTextInstructions()
Merge any adjacent instructions that create literal text nodes

Returns:
the expression after merging literal text instructions

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Description copied from class: Expression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Overrides:
iterateSubExpressions in class Expression
Returns:
an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression

Overrides:
replaceSubExpression in class Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Specified by:
copy in class Expression
Returns:
the copy of the original expression

getItemType

public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression

Overrides:
getItemType in class Instruction
Parameters:
th - the type hierarchy cache
Returns:
the data type

getCardinality

public final int getCardinality()
Determine the cardinality of the expression

Overrides:
getCardinality in class Expression
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).

createsNewNodes

public final boolean createsNewNodes()
Determine whether this instruction creates new nodes. This implementation returns true if any child instruction returns true.

Overrides:
createsNewNodes in class Instruction
Returns:
true if the instruction creates new nodes (or if it can't be proved that it doesn't)

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException
Check to ensure that this expression does not contain any updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:
checkForUpdatingSubexpressions in class Expression
Throws:
XPathException - if the expression has a non-permitted updateing subexpression

isVacuousExpression

public boolean isVacuousExpression()
Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:
isVacuousExpression in class Expression
Returns:
true if this expression is vacuous

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:
simplify in class Instruction
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException
Description copied from class: Expression
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.

If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:
typeCheck in class Expression
Parameters:
visitor - an expression visitor
contextItemType - 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 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)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException
Description copied from class: Expression
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.

Overrides:
optimize in class Expression
Parameters:
visitor - an expression visitor
contextItemType - 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)

promoteInst

protected void promoteInst(PromotionOffer offer)
                    throws XPathException
Handle promotion offers, that is, non-local tree rewrites.

Overrides:
promoteInst in class Instruction
Parameters:
offer - The type of rewrite being offered
Throws:
XPathException

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   StaticContext env,
                                   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.

Overrides:
checkPermittedContents in class Expression
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
env - the static context
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

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:
explain in class Expression
Parameters:
out - the expression presenter used to display the structure

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException
Description copied from class: Instruction
ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

Specified by:
processLeavingTail in interface TailCallReturner
Specified by:
processLeavingTail in class Instruction
Parameters:
context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
Returns:
null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
Throws:
XPathException - if a dynamic error occurs during the evaluation of the instruction

getImplementationMethod

public 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. This implementation provides both iterate() and process() methods natively.

Overrides:
getImplementationMethod in class Instruction
Returns:
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

iterate

public SequenceIterator<? extends Item> iterate(XPathContext context)
                                         throws XPathException
Iterate over the results of all the child expressions

Overrides:
iterate in class Instruction
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
Get an EventIterator over the results of all the child expressions

Overrides:
iterateEvents in class Expression
Parameters:
context - the XPath dynamic context
Returns:
an EventIterator
Throws:
XPathException - if a dynamic error occurs during expression evaluation

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

Overrides:
evaluatePendingUpdates in class Expression
Parameters:
context - the XPath dynamic evaluation context
pul - the pending update list to which the results should be written
Throws:
XPathException - if evaluation fails


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.