## net.sf.saxon.functions
Class KeyFn

    java.lang.Object
      net.sf.saxon.expr.Expression
          net.sf.saxon.expr.FunctionCall
              net.sf.saxon.functions.SystemFunction
                  net.sf.saxon.functions.KeyFn

All Implemented Interfaces:
  Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, XSLTFunction, InstructionInfoProvider

    public class KeyFn

extends SystemFunction
implements XSLTFunction

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression
`EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD`

Constructor Summary
`KeyFn()`

Method Summary
`void` `checkArguments(StaticContext env)` Method called during static type checking
`int` `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`int` `getStaticKeyFingerprint()` Get the fingerprint of the key name, if known statically.
`static KeyFn` `internalKeyCall(NamePool pool, int fingerprint, String name, Expression value, Expression doc)` Non-standard constructor to create an internal call on key() with a known key fingerprint
`SequenceIterator` `iterate(XPathContext context)` Enumerate the results of the expression
`Expression` `preEvaluate(StaticContext env)` preEvaluate: this method suppresses compile-time evaluation by doing nothing
`Expression` `simplify(StaticContext env)` Simplify: add a third implicit argument, the context document
`Expression` `typeCheck(StaticContext env, ItemType contextItemType)` Type-check the expression.

Methods inherited from class net.sf.saxon.functions.SystemFunction
`computeCardinality, display, getDetails, getErrorCodeForTypeErrors, getItemType, main, makeSystemFunction, optimize, setDetails`

Methods inherited from class net.sf.saxon.expr.FunctionCall
`getArguments, getDisplayName, getFunctionNameCode, getNumberOfArguments, iterateSubExpressions, promote, replaceSubExpression, setArguments, setFunctionNameCode`

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

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

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### KeyFn

    public KeyFn()

Method Detail

### getStaticKeyFingerprint

    public int getStaticKeyFingerprint()

  Get the fingerprint of the key name, if known statically. If not known statically, return -1.

### typeCheck

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

  Type-check the expression. This also calls preEvaluate() to evaluate the function if all the arguments are constant; functions that do not require this behavior can override the preEvaluate method.

  Overrides:
    `typeCheck` in class `FunctionCall`
  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:
    `StaticError` - if an error is discovered during this phase (typically a type error)
    `XPathException`

### internalKeyCall

    public static KeyFn internalKeyCall(NamePool pool,
                                        int fingerprint,
                                        String name,
                                        Expression value,
                                        Expression doc)

  Non-standard constructor to create an internal call on key() with a known key fingerprint

### simplify

    public Expression simplify(StaticContext env)
                        throws XPathException

  Simplify: add a third implicit argument, the context document

  Overrides:
    `simplify` in class `FunctionCall`
  Returns:
    the simplified expression
  Throws:
    `XPathException` - if an error is discovered during expression rewriting

### checkArguments

    public void checkArguments(StaticContext env)
                        throws XPathException

  Description copied from class: `SystemFunction`
  Method called during static type checking

  Overrides:
    `checkArguments` in class `SystemFunction`
  Throws:
    `XPathException`

### 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 a property bit is set, it is true, but if it is unset, the value is unknown.

  Overrides:
    `computeSpecialProperties` in class `SystemFunction`

### preEvaluate

    public Expression preEvaluate(StaticContext env)

  preEvaluate: this method suppresses compile-time evaluation by doing nothing

  Overrides:
    `preEvaluate` in class `FunctionCall`

### iterate

    public SequenceIterator iterate(XPathContext context)
                             throws XPathException

  Enumerate the results of the expression

  Specified by:
    `iterate` in interface `SequenceIterable`
  Overrides:
    `iterate` in class `Expression`
  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

Copyright (C) Michael H. Kay. All rights reserved.