Package net.sf.saxon.expr
Class PromotionOffer
java.lang.Object
net.sf.saxon.expr.PromotionOffer
PromotionOffer is an object used transiently during compilation of an expression. It contains
information passed by a containing expression to its subexpressions, when looking for subexpressions
that can be promoted to a higher level because they are not dependent on the context established
by the containing expression. The object is also used to pass back return information when the
promotion actually takes place.
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Field Summary
FieldsModifier and TypeFieldDescriptionboolean
Flag that is set if the offer has been accepted, that is, if the expression has changedint
action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT, INLINE_VARIABLE_REFERENCES, ANY_ORDER, ANY_ORDER_UNIQUEBinding[]
In the case of RANGE_INDEPENDENT and WHERE_CLAUSE, "binding" identifies the range variables whose dependencies we are looking for.When a promotion offer is made, containingExpression identifies the level to which the promotion should occur.static final int
FOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the focus.static final int
Inline variable references causes all references to a variable V to be replaced by the expression E.boolean
In the case of UNORDERED, "mustEliminateDuplicates" is a boolean that is set to true if the nodes can be delivered in any order so long as there are no duplicates (for example, as required by the count() function).boolean
In the case of FOCUS_INDEPENDENT, "promoteDocumentDependent" is a boolean that, when set to true, indicates that it is safe to promote a subexpression that depends on the context document but not on other aspects of the focus.boolean
In the case of FOCUS_INDEPENDENT, "promoteXSLTFunctions" is a boolean that, when set to true, indicates that it is safe to promote XSLT functions such as current().static final int
RANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a specified range variable.static final int
REPLACE_CURRENT causes calls to the XSLT current() function to be replaced by reference to a variable.static final int
UNORDERED indicates that the containing expression does not require the results to be delivered in any particular order. -
Constructor Summary
ConstructorsConstructorDescriptionPromotionOffer
(Optimizer optimizer) Create a PromotionOffer for use with a particular Optimizer -
Method Summary
Modifier and TypeMethodDescriptionaccept
(Expression child) Method to test whether a subexpression qualifies for promotion, and if so, to accept the promotion.Get the optimizer in use
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Field Details
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FOCUS_INDEPENDENT
public static final int FOCUS_INDEPENDENTFOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the focus. This is typically used to extract subexpressions from a filter predicate. The offer is optional - each subexpression can decide whether it's worth the trouble of promoting itself. The offer is normally passed on to subexpressions, except subexpressions that are evaluated with a different focus- See Also:
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RANGE_INDEPENDENT
public static final int RANGE_INDEPENDENTRANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a specified range variable. This is typically used to extract subexpressions from the action of a for expression or the condition of a some/every quantified expression. The offer is optional - each subexpression can decide whether it's worth the trouble of promoting itself. The offer is normally passed on to subexpressions, except subexpressions that are evaluated with a different focus or a different range variable, because these may have other dependencies that prevent their promotion.- See Also:
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INLINE_VARIABLE_REFERENCES
public static final int INLINE_VARIABLE_REFERENCESInline variable references causes all references to a variable V to be replaced by the expression E. The variable is supplied in the "binding" property; the replacement expression in the containingExpression property. A special case is where the replacement expression is a ContextItemExpression; in this case the offer is not passed on to subexpressions where the context is different.- See Also:
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UNORDERED
public static final int UNORDEREDUNORDERED indicates that the containing expression does not require the results to be delivered in any particular order. The boolean mustEliminateDuplicates is set if duplicate items in the result are not allowed.- See Also:
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REPLACE_CURRENT
public static final int REPLACE_CURRENTREPLACE_CURRENT causes calls to the XSLT current() function to be replaced by reference to a variable. The variable binding is the single member of the array bindingList- See Also:
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action
public int actionaction is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT, INLINE_VARIABLE_REFERENCES, ANY_ORDER, ANY_ORDER_UNIQUE -
promoteDocumentDependent
public boolean promoteDocumentDependentIn the case of FOCUS_INDEPENDENT, "promoteDocumentDependent" is a boolean that, when set to true, indicates that it is safe to promote a subexpression that depends on the context document but not on other aspects of the focus. This is the case, for example, in a filter expression when it is known that all the nodes selected by the expression will be in the same document - as happens when the filter is applied to a path expression. This allows subexpressions such as key() to be promoted -
promoteXSLTFunctions
public boolean promoteXSLTFunctionsIn the case of FOCUS_INDEPENDENT, "promoteXSLTFunctions" is a boolean that, when set to true, indicates that it is safe to promote XSLT functions such as current(). This flag is set when rewriting XPath expressions and is unset when rewriting XSLT templates. -
mustEliminateDuplicates
public boolean mustEliminateDuplicatesIn the case of UNORDERED, "mustEliminateDuplicates" is a boolean that is set to true if the nodes can be delivered in any order so long as there are no duplicates (for example, as required by the count() function). If this boolean is false, the nodes can be delivered in any order and duplicates are allowed (for example, as required by the boolean() function). -
bindingList
In the case of RANGE_INDEPENDENT and WHERE_CLAUSE, "binding" identifies the range variables whose dependencies we are looking for. For INLINE_VARIABLE_REFERENCES it is a single Binding that we are aiming to inline -
containingExpression
When a promotion offer is made, containingExpression identifies the level to which the promotion should occur. When a subexpression is promoted, an expression of the form let $VAR := SUB return ORIG is created, and this replaces the original containingExpression within the PromotionOffer. -
accepted
public boolean acceptedFlag that is set if the offer has been accepted, that is, if the expression has changed
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Constructor Details
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PromotionOffer
Create a PromotionOffer for use with a particular Optimizer
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Method Details
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getOptimizer
Get the optimizer in use -
accept
Method to test whether a subexpression qualifies for promotion, and if so, to accept the promotion.- Returns:
- if promotion was done, returns the expression that should be used in place of the child expression. If no promotion was done, returns null.
- Throws:
XPathException
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