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## com.saxonica.functions.map
Class MapKeys

    java.lang.Object
      net.sf.saxon.lib.ExtensionFunctionDefinition
          com.saxonica.functions.map.MapKeys

All Implemented Interfaces:
  Serializable

    public class MapKeys

extends ExtensionFunctionDefinition

Implementation of the extension function map:keys(Map) => atomicValue*

See Also:
  Serialized Form

Constructor Summary
`MapKeys()`

Method Summary
`SequenceType[]` | `getArgumentTypes()` Get the required types for the arguments of this function.
`StructuredQName` | `getFunctionQName()` Get the name of the function, as a QName.
`int` | `getMinimumNumberOfArguments()` Get the minimum number of arguments required by the function
`SequenceType` | `getResultType(SequenceType[] suppliedArgumentTypes)` Get the type of the result of the function
`ExtensionFunctionCall` | `makeCallExpression()` Create a call on this function.
`boolean` | `trustResultType()` Ask whether the result actually returned by the function can be trusted, or whether it should be checked against the declared type.

Methods inherited from class net.sf.saxon.lib.ExtensionFunctionDefinition
`dependsOnFocus, getCompilerForJava, getMaximumNumberOfArguments, hasSideEffects`

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

Constructor Detail

### MapKeys

    public MapKeys()

Method Detail

### getFunctionQName

    public StructuredQName getFunctionQName()

  Get the name of the function, as a QName.

  This method must be implemented in all subclasses

  Specified by:
    `getFunctionQName` in class `ExtensionFunctionDefinition`
  Returns:
    the function name

### getMinimumNumberOfArguments

    public int getMinimumNumberOfArguments()

  Get the minimum number of arguments required by the function

  This method must be implemented in all subclasses

  Overrides:
    `getMinimumNumberOfArguments` in class `ExtensionFunctionDefinition`
  Returns:
    the minimum number of arguments that must be supplied in a call to this function

### getArgumentTypes

    public SequenceType[] getArgumentTypes()

  Get the required types for the arguments of this function.

  This method must be implemented in all subtypes.

  Specified by:
    `getArgumentTypes` in class `ExtensionFunctionDefinition`
  Returns:
    the required types of the arguments, as defined by the function signature. Normally this should be an array of size `ExtensionFunctionDefinition.getMaximumNumberOfArguments()`; however for functions that allow a variable number of arguments, the array can be smaller than this, with the last entry in the array providing the required type for all the remaining arguments.

### getResultType

    public SequenceType getResultType(SequenceType[] suppliedArgumentTypes)

  Get the type of the result of the function

  This method must be implemented in all subtypes.

  Specified by:
    `getResultType` in class `ExtensionFunctionDefinition`
  Parameters:
    `suppliedArgumentTypes` - the static types of the supplied arguments to the function. This is provided so that a more precise result type can be returned in the common case where the type of the result depends on the types of the arguments.
  Returns:
    the return type of the function, as defined by its function signature

### trustResultType

    public boolean trustResultType()

  Ask whether the result actually returned by the function can be trusted, or whether it should be checked against the declared type.

  Overrides:
    `trustResultType` in class `ExtensionFunctionDefinition`
  Returns:
    true if the function implementation warrants that the value it returns will be an instance of the declared result type. The default value is false, in which case the result will be checked at run-time to ensure that it conforms to the declared type. If the value true is returned, but the function returns a value of the wrong type, the consequences are unpredictable.

### makeCallExpression

    public ExtensionFunctionCall makeCallExpression()

  Create a call on this function. This method is called by the compiler when it identifies a function call that calls this function.

  Specified by:
    `makeCallExpression` in class `ExtensionFunctionDefinition`

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