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Summary: Nested | Field | Method | Constr | Detail: Nested | Field | Method | Constr |
java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.instruct.Instruction
net.sf.saxon.instruct.TraceWrapper
public class TraceWrapper
extends Instruction
Field Summary |
Fields inherited from class net.sf.saxon.expr.Expression | |
EVALUATE_METHOD , ITERATE_METHOD , PROCESS_METHOD , locationId , staticProperties |
Method Summary | |
int |
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Expression |
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boolean |
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Item |
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void |
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int |
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int |
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int | |
ItemType |
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SequenceIterator |
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Iterator |
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Expression |
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TailCall |
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Expression |
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boolean |
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Expression |
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Expression |
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Methods inherited from class net.sf.saxon.instruct.Instruction | |
assembleParams , assembleTunnelParams , computeCardinality , computeSpecialProperties , createsNewNodes , dynamicError , evaluateAsString , evaluateItem , getImplementationMethod , getInstructionInfo , getInstructionNameCode , getItemType , getSourceLocator , isXSLT , iterate , process , processLeavingTail , promote , promoteInst , simplify |
public int computeDependencies()
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:
- computeDependencies in interface Expression
- Returns:
- a set of flags indicating static properties of this expression
public Expression copy()
Copy an expression. This makes a deep copy.
- Overrides:
- copy in interface Expression
- Returns:
- the copy of the original expression
public final boolean createsNewNodes()
Determine whether this instruction creates new nodes.
- Overrides:
- createsNewNodes in interface Instruction
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.
- Specified by:
- evaluateItem in interface EvaluableItem
- Overrides:
- evaluateItem in interface Instruction
- 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
public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
- Overrides:
- explain in interface Expression
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.
- Overrides:
- getCardinality in interface 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).
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 asStaticProperty.DEPENDS_ON_CONTEXT_ITEM
andStaticProperty.DEPENDS_ON_CURRENT_ITEM
. 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.
- Overrides:
- getDependencies in interface Expression
- Returns:
- a set of bit-significant flags identifying the dependencies of the expression
public int getInstructionNameCode()
- Overrides:
- getInstructionNameCode in interface Instruction
public ItemType getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
- Overrides:
- getItemType in interface Instruction
- Parameters:
th
- the type hierarchy cache
- Returns:
- the static item type of the instruction
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.
- Specified by:
- iterate in interface SequenceIterable
- Overrides:
- iterate in interface 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
public Iterator iterateSubExpressions()
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 interface Expression
- Returns:
- an iterator containing the sub-expressions of this expression
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) 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.
- Overrides:
- optimize in interface Expression
- Parameters:
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 toType.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)
public TailCall processLeavingTail(XPathContext context) throws XPathException
Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.
- Specified by:
- processLeavingTail in interface TailCallReturner
- Overrides:
- processLeavingTail in interface Instruction
- Parameters:
context
- the dynamic execution context
- Returns:
- either null, or a tail call that the caller must invoke on return
- Throws:
XPathException
-
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. This method is always called at compile time.
- Overrides:
- promote in interface Instruction
- 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
public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
- Overrides:
- replaceSubExpression in interface Expression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression
- Returns:
- true if the original subexpression is found
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.
- Overrides:
- simplify in interface Instruction
- Parameters:
visitor
- an expression visitor
- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) 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. If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and 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 interface Expression
- Parameters:
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 toType.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)