## 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:
  java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, XSLTFunction, InstructionInfo, org.xml.sax.Locator

    public class KeyFn

extends SystemFunction
implements XSLTFunction

See Also:
  Serialized Form

Field Summary

Fields inherited from class net.sf.saxon.functions.SystemFunction
`operation`

Fields inherited from class net.sf.saxon.expr.FunctionCall
`argument`

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

Constructor Summary
`KeyFn()`

Method Summary
`PathMap.PathMapNodeSet` `addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)` Add a representation of a doc() call or similar function to a PathMap.
`void` `checkArguments(ExpressionVisitor visitor)` Method called during static type checking
`int` `computeSpecialProperties()` Get the static properties of this expression (other than its type).
`Expression` `copy()` Copy an expression.
`StructuredQName` `getStaticKeyName()` Get the key name, if known statically.
`static KeyFn` `internalKeyCall(KeyDefinitionSet keySet, java.lang.String name, Expression value, Expression doc)` Non-standard constructor to create an internal call on key() with a known key definition
`SequenceIterator` `iterate(XPathContext context)` Enumerate the results of the expression
`Expression` `preEvaluate(ExpressionVisitor visitor)` preEvaluate: this method suppresses compile-time evaluation by doing nothing
`Expression` `simplify(ExpressionVisitor visitor)` Simplify: add a third implicit argument, the context document
`Expression` `typeCheck(ExpressionVisitor visitor, ItemType contextItemType)` Type-check the expression.

Methods inherited from class net.sf.saxon.functions.SystemFunction
`addContextDocumentArgument, addDocToPathMap, computeCardinality, getDetails, getErrorCodeForTypeErrors, getItemType, getRequiredType, makeSystemFunction, optimize, setDetails, useContextItemAsDefault`

Methods inherited from class net.sf.saxon.expr.FunctionCall
`addExternalFunctionCallToPathMap, checkArgumentCount, equals, explain, getArguments, getDisplayName, getFunctionName, getNumberOfArguments, hashCode, iterateSubExpressions, promote, replaceSubExpression, setArguments, setFunctionName, simplifyArguments, toString`

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

`adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Constructor Detail

### KeyFn

    public KeyFn()

Method Detail

### getStaticKeyName

    public StructuredQName getStaticKeyName()

  Get the key name, if known statically. If not known statically, return null.

  Returns:
    the key name if known, otherwise null

### typeCheck

    public Expression typeCheck(ExpressionVisitor visitor,
                                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:
    `visitor` - an expression visitor
    `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` - if an error is discovered during this phase (typically a type error)

### internalKeyCall

    public static KeyFn internalKeyCall(KeyDefinitionSet keySet,
                                        java.lang.String name,
                                        Expression value,
                                        Expression doc)

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

  Parameters:
    `keySet` - the set of KeyDefinitions (always a single KeyDefinition)
    `name` - the name allocated to the key (first argument of the function)
    `value` - the value being searched for (second argument of the function)
    `doc` - the document being searched (third argument)
  Returns:
    a call on the key() function

### simplify

    public Expression simplify(ExpressionVisitor visitor)
                        throws XPathException

  Simplify: add a third implicit argument, the context document

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

### checkArguments

    public void checkArguments(ExpressionVisitor visitor)
                        throws XPathException

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

  Overrides:
    `checkArguments` in class `SystemFunction`
  Parameters:
    `visitor` - the expression visitor
  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`
  Returns:
    the special properties, as a bit-significant integer

### preEvaluate

    public Expression preEvaluate(ExpressionVisitor visitor)

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

  Overrides:
    `preEvaluate` in class `FunctionCall`
  Parameters:
    `visitor` - the expression visitor
  Returns:
    the result of the early evaluation, or the original expression, or potentially a simplified expression

### addToPathMap

    public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                               PathMap.PathMapNodeSet pathMapNodeSet)

  Add a representation of a doc() call or similar function to a PathMap. This is a convenience method called by the addToPathMap() methods for doc(), document(), collection() and similar functions. These all create a new root expression in the path map.

  Overrides:
    `addToPathMap` in class `Expression`
  Parameters:
    `pathMap` - the PathMap to which the expression should be added
    `pathMapNodeSet` -
  Returns:
    the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

### copy

    public Expression copy()

  Copy an expression. This makes a deep copy.

  Overrides:
    `copy` in class `SystemFunction`
  Returns:
    the copy of the original expression

### 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) Saxonica Limited. All rights reserved.