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.
- addToPathMap in interface Expression
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
-
- the pathMapNode representing the focus established by this expression, in the case where this
expression is the first operand of a path expression or filter 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.
computeSpecialProperties
public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is
bit-significant. 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.
- computeSpecialProperties in interface Expression
copy
public Expression copy()
Copy an expression. This makes a deep copy.
- copy in interface Expression
- the copy of the original expression
explain
public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree
is written to the supplied output destination.
- explain in interface Expression
getBaseExpression
public Expression getBaseExpression()
Get the expression defining the sequence being sorted
- the expression whose result is to be sorted
getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible
- getItemType in interface Expression
th
- the type hierarchy cache
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE,
or Type.ITEM (meaning not known in advance)
hasLoopingSubexpression
public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether
the evaluation of the parent expression causes the child expression to be
evaluated repeatedly
- hasLoopingSubexpression in interface Expression
child
- the immediate subexpression
- true if the child expression is evaluated repeatedly
isSortKey
public boolean isSortKey(Expression child)
Test whether a given expression is one of the sort keys
child
- the given expression
- true if the given expression is one of the sort keys
iterateSubExpressions
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.
- iterateSubExpressions in interface Expression
- an iterator containing the sub-expressions of this expression
optimize
public Expression optimize(ExpressionVisitor visitor,
ItemType contextItemType)
throws XPathException
Perform optimisation of an expression and its subexpressions.
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 interface 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
- the original expression, rewritten if appropriate to optimize execution
XPathException
- if an error is discovered during this phase
(typically a type error)
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 not accepted - this is appropriate in the case of simple expressions
such as constant values and variable references where promotion would give no performance
advantage. This method is always called at compile time.
- promote in interface Expression
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
- if the offer is not accepted, return this expression unchanged.
Otherwise return the result of rewriting the expression to promote
this subexpression
replaceSubExpression
public boolean replaceSubExpression(Expression original,
Expression replacement)
Replace one subexpression by a replacement subexpression
- replaceSubExpression in interface Expression
original
- the original subexpressionreplacement
- the replacement subexpression
- true if the original subexpression is found