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java.lang.Object net.sf.saxon.expr.Expression net.sf.saxon.expr.Assignation net.sf.saxon.expr.LetExpression
public class LetExpression
A LetExpression is modelled on the XQuery syntax let $x := expr return expr. This syntax is not available in the surface XPath language, but it is used internally in an optimized expression tree.
Field Summary |
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Fields inherited from class net.sf.saxon.expr.Assignation |
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action, requiredType, sequence, slotNumber, variableName |
Fields inherited from class net.sf.saxon.expr.Expression |
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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 | |
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LetExpression()
Create a LetExpression |
Method Summary | |
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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 |
computeCardinality()
Determine the static cardinality of the expression |
int |
computeSpecialProperties()
Get the static properties of this expression (other than its type). |
Expression |
copy()
Copy an expression. |
boolean |
effectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression. |
ValueRepresentation |
eval(XPathContext context)
Evaluate the variable. |
Item |
evaluateItem(XPathContext context)
Evaluate the expression as a singleton |
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 |
getEvaluationMode()
|
String |
getExpressionName()
Get a name identifying the kind of expression, in terms meaningful to a user. |
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. |
ItemType |
getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible |
boolean |
implementsStaticTypeCheck()
Determine whether this expression implements its own method for static type checking |
boolean |
isVacuousExpression()
Determine whether this is a vacuous expression as defined in the XQuery update specification |
SequenceIterator |
iterate(XPathContext context)
Iterate over the result of the expression to return a sequence of items |
EventIterator |
iterateEvents(XPathContext context)
Iterate over the result of the expression to return a sequence of events |
int |
markTailFunctionCalls(StructuredQName qName,
int arity)
Mark tail function calls |
Expression |
optimize(ExpressionVisitor visitor,
ExpressionVisitor.ContextItemType contextItemType)
Perform optimisation of an expression and its subexpressions. |
void |
process(XPathContext context)
Process this expression as an instruction, writing results to the current outputter |
TailCall |
processLeavingTail(XPathContext context)
ProcessLeavingTail: called to do the real work of this instruction. |
Expression |
promote(PromotionOffer offer,
Expression parent)
Promote this expression if possible |
void |
setEvaluationMode(int evaluationMode)
|
void |
setRefCount(int refCount)
|
Expression |
staticTypeCheck(SequenceType req,
boolean backwardsCompatible,
RoleLocator role,
TypeCheckerEnvironment visitor)
Static type checking for let expressions is delegated to the expression itself, and is performed on the "action" expression, to allow further delegation to the branches of a conditional |
String |
toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. |
Expression |
typeCheck(ExpressionVisitor visitor,
ExpressionVisitor.ContextItemType contextItemType)
Type-check the expression. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public LetExpression()
Method Detail |
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public String getExpressionName()
getExpressionName
in class Expression
public void setRefCount(int refCount)
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
typeCheck
in class Expression
visitor
- an expression visitorcontextItemType
- 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
XPathException
- if an error is discovered during this phase
(typically a type error)public boolean implementsStaticTypeCheck()
implementsStaticTypeCheck
in class Expression
public Expression staticTypeCheck(SequenceType req, boolean backwardsCompatible, RoleLocator role, TypeCheckerEnvironment visitor) throws XPathException
staticTypeCheck
in class Expression
req
- the required typebackwardsCompatible
- true if backwards compatibility mode appliesrole
- the role of the expression in relation to the required typevisitor
- an expression visitor
XPathException
- if failures occur, for example if the static type of one branch of the conditional
is incompatible with the required typepublic Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
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.
optimize
in class Expression
visitor
- an expression visitorcontextItemType
- 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
XPathException
- if an error is discovered during this phase
(typically a type error)public boolean isVacuousExpression()
isVacuousExpression
in class Expression
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException
checkPermittedContents
in class Expression
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 typeenv
- the static contextwhole
- 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
XPathException
- if the value delivered by this expression cannot be part of the content model
of the given typepublic IntegerValue[] getIntegerBounds()
getIntegerBounds
in class Expression
public SequenceIterator iterate(XPathContext context) throws XPathException
iterate
in class Expression
context
- supplies the context for evaluation
XPathException
- if any dynamic error occurs evaluating the
expressionpublic EventIterator iterateEvents(XPathContext context) throws XPathException
iterateEvents
in class Expression
context
- The dynamic evaluation context
XPathException
- if a dynamic error occurs during expression evaluationpublic ValueRepresentation eval(XPathContext context) throws XPathException
context
- the dynamic evaluation context
XPathException
public Item evaluateItem(XPathContext context) throws XPathException
evaluateItem
in class Expression
context
- The context in which the expression is to be evaluated
XPathException
- if any dynamic error occurs evaluating the
expressionpublic boolean effectiveBooleanValue(XPathContext context) throws XPathException
effectiveBooleanValue
in class Expression
context
- The context in which the expression is to be evaluated
XPathException
- if any dynamic error occurs evaluating the
expressionpublic void process(XPathContext context) throws XPathException
process
in class Expression
context
- The dynamic context, giving access to the current node,
the current variables, etc.
XPathException
- if a dynamic error occurspublic ItemType getItemType(TypeHierarchy th)
getItemType
in class Expression
th
- the type hierarchy cache
public int computeCardinality()
computeCardinality
in class Expression
StaticProperty.ALLOWS_ZERO_OR_ONE
,
StaticProperty.EXACTLY_ONE
, StaticProperty.ALLOWS_ONE_OR_MORE
,
StaticProperty.ALLOWS_ZERO_OR_MORE
public int computeSpecialProperties()
computeSpecialProperties
in class Expression
public int markTailFunctionCalls(StructuredQName qName, int arity)
markTailFunctionCalls
in class Expression
qName
- the name of the functionarity
- the arity (number of parameters) of the function
UserFunctionCall.NOT_TAIL_CALL
if no tail call was found;
UserFunctionCall.FOREIGN_TAIL_CALL
if a tail call on a different function was found;public Expression promote(PromotionOffer offer, Expression parent) throws XPathException
promote
in class Assignation
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 expressionparent
- the containing expression in the expression tree
XPathException
- if any error is detectedpublic Expression copy()
copy
in class Expression
public TailCall processLeavingTail(XPathContext context) throws XPathException
processLeavingTail
in interface TailCallReturner
context
- The dynamic context of the transformation, giving access to the current node,
the current variables, etc.
XPathException
- if a dynamic error occurs during the evaluation
of the instructionpublic void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException
evaluatePendingUpdates
in class Expression
context
- the XPath dynamic evaluation contextpul
- the pending update list to which the results should be written
XPathException
- if evaluation failspublic String toString()
toString
in class Expression
public void explain(ExpressionPresenter out)
explain
in class Expression
out
- the expression presenter used to display the structurepublic void setEvaluationMode(int evaluationMode)
public int getEvaluationMode()
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