Package net.sf.saxon.expr.parser

Class LoopLifter

java.lang.Object

net.sf.saxon.expr.parser.LoopLifter

public class LoopLifter
extends Object

Class to handle loop-lifting optimization, that is, extraction of subexpressions appearing within a loop when there is no dependency on the controlling variable of the loop. This handles both focus-dependent loops (such as xsl:for-each) and variable-dependent loops (such as XPath for-expressions), and also takes into account specialist loops such as xsl:for-each-group, xsl:merge, and xsl:analyze-string. The class is instantiated to perform optimization of a component such as a function or template, and it contains temporary instance-level data pertaining to that function or template.

Constructor Summary

Constructors

Constructor	Description
LoopLifter(Expression root, Configuration config, boolean streaming)

Method Summary

Modifier and Type	Method	Description
void	gatherInfo(Expression exp)	Gather information about an expression.
Expression	getRoot()
static Expression	process(Expression exp, ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)	Apply loop-lifting to an expression (typically the body of a template or function)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LoopLifter

public LoopLifter(Expression root,
 Configuration config,
 boolean streaming)

Method Details

process

public static Expression process(Expression exp,
 ExpressionVisitor visitor,
 ContextItemStaticInfo contextInfo)
                          throws XPathException

Apply loop-lifting to an expression (typically the body of a template or function)

Parameters:

exp - the expression to which loop lifting is applied

visitor - the expression visitor

contextInfo - the static type of the context item

Returns:

the optimized expression

Throws:

XPathException - if any error occurs

getRoot

public Expression getRoot()

gatherInfo

public void gatherInfo(Expression exp)

Gather information about an expression. The information (in the form of an ExpInfo object) is added to the expInfoMap, which is indexed by expression.

Parameters:

exp - the expression for which information is required