net.sf.saxon.expr
Class UnaryExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.UnaryExpression

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

Direct Known Subclasses:

AtomicSequenceConverter, Atomizer, CardinalityChecker, CastableExpression, CastExpression, DocumentSorter, FirstItemExpression, InstanceOfExpression, ItemChecker, LazyExpression, NumericPromoter, Reverser, SingletonAtomizer, StringMirrorExpression, UntypedAtomicConverter

public abstract class UnaryExpression

extends ComputedExpression

Unary Expression: an expression taking a single operand expression

See Also:

Serialized Form

Field Summary

protected Expression

operand

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

UnaryExpression(Expression p0)

Method Summary

int	computeCardinality() Determine the static cardinality.
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
void	display(int level, NamePool pool, java.io.PrintStream out) Diagnostic print of expression structure
protected abstract java.lang.String	displayOperator(NamePool pool) Give a string representation of the operator for use in diagnostics
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
Expression	getBaseExpression()
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression, if possible.
int	hashCode() get HashCode for comparing two expressions.
java.util.Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Promote this expression if possible
Expression	simplify(StaticContext env) Simplify an expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression.

Methods inherited from class net.sf.saxon.expr.ComputedExpression

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Field Detail

operand

protected Expression operand

Constructor Detail

UnaryExpression

public UnaryExpression(Expression p0)

Method Detail

getBaseExpression

public Expression getBaseExpression()

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression. Default implementation for unary operators that accept any kind of operand

Parameters:

env - the static context of the expression

contextItemType - 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 Type.ITEM_TYPE

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

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.

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 expression

contextItemType - 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 Type.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

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

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

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

computeSpecialProperties

public int computeSpecialProperties()

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:

computeSpecialProperties in class ComputedExpression

computeCardinality

public int computeCardinality()

Determine the static cardinality. Default implementation returns the cardinality of the operand

Specified by:

computeCardinality in class ComputedExpression

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the expression, if possible. The default implementation for unary expressions returns the item type of the operand

Parameters:

th -

Returns:

the item type of the items in the result sequence, insofar as this is known statically.

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

hashCode

public int hashCode()

get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)

Diagnostic print of expression structure

Parameters:

level - indentation level for this expression

pool - NamePool used to expand any names appearing in the expression

out - Output destination

displayOperator

protected abstract java.lang.String displayOperator(NamePool pool)

Give a string representation of the operator for use in diagnostics

Returns:

the operator, as a string