net.sf.saxon.expr
Class PromotionOffer
public
class
PromotionOffer
extends Object
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.
Field Summary |
boolean | accepted
Flag that is set if the offer has been accepted, that is, if the expression has changed |
int | action
action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT,
INLINE_VARIABLE_REFERENCES, UNORDERED, EXTRACT_GLOBAL_VARIABLES |
Binding[] | bindingList
In the case of RANGE_INDEPENDENT, "binding" identifies the range variables whose dependencies
we are looking for. |
Expression | containingExpression
When a promotion offer is made, containingExpression identifies the level to which the promotion
should occur. |
static int | EXTRACT_GLOBAL_VARIABLES
EXTRACT_GLOBAL_VARIABLES identifies subexpressions that are not constant, but have no dependencies
other than on global variables or parameters (they must also be non-creative). |
static int | FOCUS_INDEPENDENT
FOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the
focus. |
static int | INLINE_VARIABLE_REFERENCES
Inline variable references causes all references to a variable V to be replaced by the
expression E. |
boolean | promoteDocumentDependent
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 | promoteXSLTFunctions
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(). |
boolean | retainAllNodes
In the case of UNORDERED, "retainAllNodes" is a boolean that is set to
true if the nodes can be delivered in any order so long as the right number of nodes
are delivered. |
static int | RANGE_INDEPENDENT
RANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a
specified range variable. |
static int | REPLACE_CURRENT
REPLACE_CURRENT causes calls to the XSLT current() function to be replaced by
reference to a variable. |
static int | UNORDERED
UNORDERED indicates that the containing expression does not require the results
to be delivered in any particular order. |
ExpressionVisitor | visitor
The expression visitor in use |
public boolean accepted
Flag that is set if the offer has been accepted, that is, if the expression has changed
public int action
action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT,
INLINE_VARIABLE_REFERENCES, UNORDERED, EXTRACT_GLOBAL_VARIABLES
In the case of RANGE_INDEPENDENT, "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
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.
public static final int EXTRACT_GLOBAL_VARIABLES
EXTRACT_GLOBAL_VARIABLES identifies subexpressions that are not constant, but have no dependencies
other than on global variables or parameters (they must also be non-creative). Such expressions can
be extracted from a function or template and converted into global variables. This optimization is done
in Saxon-EE only.
public static final int FOCUS_INDEPENDENT
FOCUS_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
public static final int INLINE_VARIABLE_REFERENCES
Inline 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.
public boolean promoteDocumentDependent
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. 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
public boolean promoteXSLTFunctions
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(). This flag is set when rewriting XPath expressions
and is unset when rewriting XSLT templates.
public boolean retainAllNodes
In the case of UNORDERED, "retainAllNodes" is a boolean that is set to
true if the nodes can be delivered in any order so long as the right number of nodes
are delivered. If this boolean is false, the caller doesn't care whether duplicate nodes
are retained or whether they are eliminated.
public static final int RANGE_INDEPENDENT
RANGE_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.
public static final int REPLACE_CURRENT
REPLACE_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
public static final int UNORDERED
UNORDERED 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.
The expression visitor in use
Create a PromotionOffer for use with a particular Optimizer
Parameters: optimizer the optimizer
Method to test whether a subexpression qualifies for promotion, and if so, to
accept the promotion.
Parameters: parent child the subexpression in question
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. If promotion is
determined not to be necessary for this subtree, returns the supplied child expression
unchanged
Get the optimizer in use
Returns: the optimizer