Class SimpleExpression
- java.lang.Object
-
- net.sf.saxon.expr.ComputedExpression
-
- net.sf.saxon.expr.SimpleExpression
-
- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,Expression
,InstructionInfoProvider
public abstract class SimpleExpression extends ComputedExpression
An abstract implementation of Expression designed to make it easy to implement new expressions, in particular, expressions to support extension instructions.- See Also:
- Serialized Form
-
-
Field Summary
Fields Modifier and Type Field Description protected Expression[]
arguments
static Expression[]
NO_ARGUMENTS
-
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
Constructors Constructor Description SimpleExpression()
Constructor
-
Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
computeCardinality()
Determine the static cardinality of the expression.int
computeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.void
display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure.Item
evaluateItem(XPathContext context)
Evaluate an expression as a single item.java.lang.String
getExpressionType()
Return a distinguishing name for the expression, for use in diagnostics.ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression.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.Expression
optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.void
process(XPathContext context)
Process the instruction, without returning any tail callsExpression
promote(PromotionOffer offer)
Offer promotion for this subexpression.boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpressionvoid
setArguments(Expression[] sub)
Set the immediate sub-expressions of this expression.Expression
simplify(StaticContext env)
Simplify the expressionExpression
typeCheck(StaticContext env, ItemType contextItemType)
Perform type checking of an expression and its subexpressions.-
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
-
-
-
-
Field Detail
-
NO_ARGUMENTS
public static final Expression[] NO_ARGUMENTS
-
arguments
protected Expression[] arguments
-
-
Method Detail
-
setArguments
public void setArguments(Expression[] sub)
Set the immediate sub-expressions of this expression.- Parameters:
sub
- an array containing the sub-expressions of this expression
-
iterateSubExpressions
public java.util.Iterator iterateSubExpressions()
Get the immediate sub-expressions of this expression.- Specified by:
iterateSubExpressions
in interfaceExpression
- Overrides:
iterateSubExpressions
in classComputedExpression
- Returns:
- an array containing the sub-expressions of this expression
-
replaceSubExpression
public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression- Specified by:
replaceSubExpression
in interfaceContainer
- Overrides:
replaceSubExpression
in classComputedExpression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
-
simplify
public Expression simplify(StaticContext env) throws XPathException
Simplify the expression- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classComputedExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
-
typeCheck
public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
Description copied from interface:Expression
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.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 may not be accurately known if they have not been explicitly declared.
If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.
- Parameters:
env
- the static context of the expressioncontextItemType
- 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 toType.ITEM_TYPE
- Returns:
- the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
- Throws:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
-
optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
Description copied from interface:Expression
Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.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.
- Parameters:
opt
- the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.env
- the static context of the expressioncontextItemType
- 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 toType.ITEM_TYPE
- Returns:
- the original expression, rewritten if appropriate to optimize execution
- Throws:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
-
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.- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classComputedExpression
- Parameters:
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- Returns:
- if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
- Throws:
XPathException
- if any error is detected
-
getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression. This implementation returns "item()", which can be overridden in a subclass.- Parameters:
th
-- Returns:
- the data type
-
computeCardinality
public int computeCardinality()
Determine the static cardinality of the expression. This implementation returns "zero or more", which can be overridden in a subclass.- Specified by:
computeCardinality
in classComputedExpression
-
computeDependencies
public int computeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.- Overrides:
computeDependencies
in classComputedExpression
- Returns:
- the depencies, as a bit-mask
-
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 interfaceExpression
- Overrides:
evaluateItem
in classComputedExpression
- 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 interfaceExpression
- Overrides:
iterate
in classComputedExpression
- 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
-
process
public void process(XPathContext context) throws XPathException
Process the instruction, without returning any tail calls- Specified by:
process
in interfaceExpression
- Overrides:
process
in classComputedExpression
- Parameters:
context
- The dynamic context, giving access to the current node, the current variables, etc.- Throws:
XPathException
-
display
public void display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure. The expression is written to the System.err output stream- Parameters:
level
- indentation level for this expressionout
-config
-
-
getExpressionType
public java.lang.String getExpressionType()
Return a distinguishing name for the expression, for use in diagnostics. By default the class name is used.
-
-