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The XSLT and XQuery Processor
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr.instruct;
import net.sf.saxon.event.Outputter;
import net.sf.saxon.expr.*;
import net.sf.saxon.expr.parser.ContextItemStaticInfo;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.expr.parser.RebindingMap;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
/**
* A compiled xsl:sequence instruction. Used only when strict streamability analysis is
* required; the instruction differs from its operand only by being marked as an instruction,
* which is sometimes relevant for streamability analysis. Used for xsl:sequence and also
* for xsl:map and xsl:map-entry; and also to wrap expressions in text value templates.
*/
public class SequenceInstr extends UnaryExpression {
/**
* Create the instruction
*
* @param base the base expression
*/
public SequenceInstr(Expression base) {
super(base);
}
/**
* Ask whether this expression is an instruction. In XSLT streamability analysis this
* is used to distinguish constructs corresponding to XSLT instructions from other constructs.
*
* @return true if this construct originates as an XSLT instruction
*/
@Override
public boolean isInstruction() {
return true;
}
/**
* Get the usage (in terms of streamability analysis) of the single operand
*
* @return the operand usage
*/
@Override
protected OperandRole getOperandRole() {
return new OperandRole(0, OperandUsage.TRANSMISSION);
}
/**
* Simplify an expression. This performs any static optimization (by rewriting the expression
* as a different expression). The default implementation simplifies its operands.
*
* @return the simplified expression (or the original if unchanged, or if modified in-situ)
* @throws XPathException if an error is discovered during expression
* rewriting
*/
// @Override
// public Expression simplify() throws XPathException {
// return getBaseExpression();
// }
/**
* Type-check the expression. Default implementation for unary operators that accept
* any kind of operand
*/
/*@NotNull*/
@Override
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException {
getOperand().typeCheck(visitor, contextInfo);
return this;
}
/**
* 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.
*
* @param visitor an expression visitor
* @param contextInfo 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
* {@link net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException {
getOperand().optimize(visitor, contextInfo);
return this;
}
/*@NotNull*/
@Override
public Expression copy(RebindingMap rebindings) {
return new SequenceInstr(getBaseExpression().copy(rebindings));
}
/**
* An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
* This method indicates which of these methods is provided directly. The other methods will always be available
* indirectly, using an implementation that relies on one of the other methods.
*
* @return the implementation method, for example {@link #ITERATE_METHOD} or {@link #EVALUATE_METHOD} or
* {@link #PROCESS_METHOD}
*/
@Override
public int getImplementationMethod() {
return getBaseExpression().getImplementationMethod();
}
/**
* Get a name identifying the kind of expression, in terms meaningful to a user.
*
* @return a name identifying the kind of expression, in terms meaningful to a user.
* The name will always be in the form of a lexical XML QName, and should match the name used
* in export() output displaying the expression.
*/
@Override
public String getExpressionName() {
return "sequence";
}
/**
* Process the instruction, without returning any tail calls
*
*
* @param output the destination for the result
* @param context The dynamic context, giving access to the current node,
* the current variables, etc.
* @throws XPathException if a dynamic error occurs
*/
@Override
public void process(Outputter output, XPathContext context) throws XPathException {
getBaseExpression().process(output, context);
}
/**
* 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.
*
* @param context supplies the context for evaluation
* @return a SequenceIterator that can be used to iterate over the result
* of the expression
* @throws XPathException if any dynamic error occurs evaluating the
* expression
*/
@Override
public SequenceIterator iterate(XPathContext context) throws XPathException {
return getBaseExpression().iterate(context);
}
@Override
public void export(ExpressionPresenter out) throws XPathException {
getBaseExpression().export(out);
}
/**
* Get the (partial) name of a class that supports streaming of this kind of expression
*
* @return the partial name of a class that can be instantiated to provide streaming support in Saxon-EE,
* or null if there is no such class
*/
@Override
public String getStreamerName() {
return "SequenceInstr";
}
}