net.sf.saxon.instruct
Class TraceWrapper

java.lang.Object
  extended bynet.sf.saxon.expr.ComputedExpression
      extended bynet.sf.saxon.instruct.Instruction
          extended bynet.sf.saxon.instruct.TraceWrapper
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator
Direct Known Subclasses:
TraceExpression, TraceInstruction

public class TraceWrapper
extends Instruction

This class is a tracing wrapper around any expression: it delivers the same result as the wrapped expression, but traces its evaluation to a TraceListener

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
 
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
TraceWrapper()
           
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          I Perform static analysis of an expression and its subexpressions.
 int computeDependencies()
          Get the static properties of this expression (other than its type).
 boolean createsNewNodes()
          Determine whether this instruction creates new nodes.
 void display(int level, NamePool pool, java.io.PrintStream out)
          Diagnostic print of expression structure.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 int getCardinality()
          Determine the static cardinality of the expression.
 int getDependencies()
          Determine which aspects of the context the expression depends on.
 int getInstructionNameCode()
          Get the namecode of the instruction for use in diagnostics
 ItemType getItemType()
          Get the item type of the items returned by evaluating this instruction
 SequenceIterator iterate(XPathContext context)
          Return an Iterator to iterate over the values of a sequence.
 java.util.Iterator iterateSubExpressions()
          Get the immediate sub-expressions of this expression.
 TailCall processLeavingTail(XPathContext context)
          Execute this instruction, with the possibility of returning tail calls if there are any.
 Expression simplify(StaticContext env)
          Simplify an expression.
 
Methods inherited from class net.sf.saxon.instruct.Instruction
appendItem, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, getImplementationMethod, getInstructionInfo, getSourceLocator, isXSLT, process, promote, promoteInst
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeStaticProperties, dynamicError, dynamicError, getColumnNumber, getConstructType, getExecutable, getIntrinsicDependencies, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, typeError, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getLineNumber, getPublicId, getSystemId
 

Constructor Detail

TraceWrapper

public TraceWrapper()
Method Detail

simplify

public Expression simplify(StaticContext env)
                    throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:
simplify in interface Expression
Specified by:
simplify in class Instruction
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

analyze

public Expression analyze(StaticContext env,
                          ItemType contextItemType)
                   throws XPathException
I Perform static analysis of an expression and its subexpressions.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables will only be accurately known if they have been explicitly declared.

Specified by:
analyze in interface Expression
Specified by:
analyze in class Instruction
Parameters:
env - the static context of the expression
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException
Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.

Specified by:
processLeavingTail in class Instruction
Parameters:
context - the dynamic execution context
Returns:
either null, or a tail call that the caller must invoke on return
Throws:
XPathException

getItemType

public ItemType getItemType()
Get the item type of the items returned by evaluating this instruction

Specified by:
getItemType in interface Expression
Overrides:
getItemType in class Instruction
Returns:
the static item type of the instruction

getCardinality

public int getCardinality()
Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.

Specified by:
getCardinality in interface Expression
Overrides:
getCardinality in class ComputedExpression
Returns:
one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getDependencies

public int getDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.

Specified by:
getDependencies in interface Expression
Overrides:
getDependencies in class ComputedExpression
Returns:
a set of bit-significant flags identifying the dependencies of the expression

createsNewNodes

public final boolean createsNewNodes()
Determine whether this instruction creates new nodes. This implementation returns true unconditionally. This suppresses optimizations, which is appropriate when tracing.

Overrides:
createsNewNodes in class Instruction

computeDependencies

public int computeDependencies()
Get the static properties of this expression (other than its type). The result is bit-signficant. 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.

Overrides:
computeDependencies in class ComputedExpression
Returns:
a set of flags indicating static properties of this expression

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Specified by:
evaluateItem in interface Expression
Overrides:
evaluateItem in class Instruction
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
Throws:
XPathException - if any dynamic error occurs evaluating the expression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
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.

Specified by:
iterate in interface Expression
Overrides:
iterate in class Instruction
Parameters:
context - supplies the context for evaluation
Returns:
a SequenceIterator that can be used to iterate over the result of the expression
Throws:
XPathException - if any dynamic error occurs evaluating the expression

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()
Description copied from class: ComputedExpression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Specified by:
iterateSubExpressions in interface Expression
Overrides:
iterateSubExpressions in class ComputedExpression
Returns:
an iterator containing the sub-expressions of this expression

getInstructionNameCode

public int getInstructionNameCode()
Description copied from class: Instruction
Get the namecode of the instruction for use in diagnostics

Overrides:
getInstructionNameCode in class Instruction

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)
Diagnostic print of expression structure. The expression is written to the System.err output stream

Parameters:
level - indentation level for this expression
out -
pool - NamePool used to expand any names appearing in the expression