Package net.sf.saxon.expr.sort

## Class MergeInstr

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.instruct.Instruction
    - - net.sf.saxon.expr.sort.MergeInstr

- All Implemented Interfaces:
    `ExportAgent`, `TailCallReturner`, `Locatable`, `IdentityComparable`, `Traceable`

      public class MergeInstr
      extends Instruction

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class | Description
    --- | --- | ---
    `static class` | `MergeInstr.MergeKeyMappingFunction` | Mapping function for items encountered during the merge; the mapping function wraps the merged item and its merge keys into a single composite object
    `static class` | `MergeInstr.MergeSource` | Inner class representing one merge source

  - ### Field Summary

    Fields
    Modifier and Type | Field | Description
    --- | --- | ---
    `protected AtomicComparer[]` | `comparators` |
    `protected MergeInstr.MergeSource[]` | `mergeSources` |

    - ### Fields inherited from class net.sf.saxon.expr.Expression

      `EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD`

  - ### Constructor Summary

    Constructors
    Constructor | Description
    --- | ---
    `MergeInstr()` |

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `boolean` | `allowExtractingCommonSubexpressions()` | Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself.
    `void` | `checkPermittedContents​(SchemaType parentType, boolean whole)` | Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
    `Expression` | `copy​(RebindingMap rebindings)` | Copy an expression.
    `void` | `export​(ExpressionPresenter out)` | Diagnostic print of expression structure.
    `void` | `fixupGroupReferences()` |
    `Expression` | `getAction()` |
    `ItemOrderComparer` | `getComparer​(SortKeyDefinitionList sKeys, AtomicComparer[] comps)` |
    `Expression` | `getGroupingKey()` | Get the grouping key expression expression (the group-by or group-adjacent expression, or a PatternSponsor containing the group-starting-with or group-ending-with expression)
    `int` | `getInstructionNameCode()` | Get the namecode of the instruction for use in diagnostics
    `ItemType` | `getItemType()` | Get the item type of the items returned by evaluating this instruction
    `MergeInstr.MergeSource[]` | `getMergeSources()` |
    `java.lang.String` | `getStreamerName()` | Get the (partial) name of a class that supports streaming of this kind of expression
    `MergeInstr` | `init​(MergeInstr.MergeSource[] mSources, Expression action)` | Initialise the merge instruction
    `SequenceIterator` | `iterate​(XPathContext context)` | Return an Iterator to iterate over the values of a sequence.
    `boolean` | `mayCreateNewNodes()` | Determine whether this instruction creates new nodes.
    `java.lang.Iterable<Operand>` | `operands()` | Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
    `Expression` | `optimize​(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` | Perform optimisation of an expression and its subexpressions.
    `void` | `prepareForStreaming()` |
    `TailCall` | `processLeavingTail​(Outputter output, XPathContext context)` | ProcessLeavingTail: called to do the real work of this instruction.
    `void` | `setAction​(Expression action)` |
    `Expression` | `typeCheck​(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)` | Perform type checking of an expression and its subexpressions.

    - ### Methods inherited from class net.sf.saxon.expr.instruct.Instruction

      `alwaysCreatesNewNodes, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, evaluateItem, getExpressionName, getImplementationMethod, getNetCost, getSourceLocator, isInstruction, isXSLT, process, someOperandCreatesNewNodes`

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

      `addToPathMap, adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, computeDependencies, computeHashCode, computeStaticProperties, dynamicError, effectiveBooleanValue, equals, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toShortString, toString, typeCheckChildren, typeError, unordered, verifyParentPointers`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface net.sf.saxon.trace.Traceable

      `gatherProperties`

- - ### Field Detail

    - #### mergeSources

          protected MergeInstr.MergeSource[] mergeSources

    - #### comparators

          protected AtomicComparer[] comparators

  - ### Constructor Detail

    - #### MergeInstr

          public MergeInstr()

  - ### Method Detail

    - #### init

          public MergeInstr init​(MergeInstr.MergeSource[] mSources,
                                 Expression action)

      Initialise the merge instruction
      Parameters:
        `mSources` - the set of merge source definitions
        `action` - the action to be performed on each group of items with identical merge keys
      Returns:
        the merge instruction (to allow call chaining)

    - #### getMergeSources

          public MergeInstr.MergeSource[] getMergeSources()

    - #### setAction

          public void setAction​(Expression action)

    - #### getAction

          public Expression getAction()

    - #### getInstructionNameCode

          public int getInstructionNameCode()

      Get the namecode of the instruction for use in diagnostics
      Overrides:
        `getInstructionNameCode` in class `Instruction`
      Returns:
        a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

    - #### checkPermittedContents

          public void checkPermittedContents​(SchemaType parentType,
                                             boolean whole)
                                      throws XPathException

      Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.
      Overrides:
        `checkPermittedContents` in class `Expression`
      Parameters:
        `parentType` - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type
        `whole` - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content
      Throws:
        `XPathException` - if the value delivered by this expression cannot be part of the content model of the given type

    - #### allowExtractingCommonSubexpressions

          public boolean allowExtractingCommonSubexpressions()

      Ask whether common subexpressions found in the operands of this expression can be extracted and evaluated outside the expression itself. The result is irrelevant in the case of operands evaluated with a different focus, which will never be extracted in this way, even if they have no focus dependency.
      Overrides:
        `allowExtractingCommonSubexpressions` in class `Expression`
      Returns:
        false for this kind of expression

    - #### getItemType

          public ItemType getItemType()

      Get the item type of the items returned by evaluating this instruction
      Overrides:
        `getItemType` in class `Instruction`
      Returns:
        the static item type of the instruction

    - #### typeCheck

          public Expression typeCheck​(ExpressionVisitor visitor,
                                      ContextItemStaticInfo contextInfo)
                               throws XPathException

      Description copied from class: `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.

      Overrides:
        `typeCheck` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextInfo` - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.
      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)

    - #### fixupGroupReferences

          public void fixupGroupReferences()

    - #### mayCreateNewNodes

          public final boolean mayCreateNewNodes()

      Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).
      Overrides:
        `mayCreateNewNodes` in class `Instruction`
      Returns:
        true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)

    - #### optimize

          public Expression optimize​(ExpressionVisitor visitor,
                                     ContextItemStaticInfo contextInfo)
                              throws XPathException

      Description copied from class: `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.

      Overrides:
        `optimize` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextInfo` - 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:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### prepareForStreaming

          public void prepareForStreaming()
                                   throws XPathException

      Overrides:
        `prepareForStreaming` in class `Expression`
      Throws:
        `XPathException`

    - #### iterate

          public SequenceIterator iterate​(XPathContext context)
                                   throws XPathException

      Description copied from class: `Instruction`
      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.
      Overrides:
        `iterate` in class `Instruction`
      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

    - #### operands

          public java.lang.Iterable<Operand> operands()

      Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.
      Specified by:
        `operands` in class `Instruction`
      Returns:
        an iterator containing the sub-expressions of this expression

    - #### getGroupingKey

          public Expression getGroupingKey()

      Get the grouping key expression expression (the group-by or group-adjacent expression, or a PatternSponsor containing the group-starting-with or group-ending-with expression)
      Returns:
        the expression used to calculate grouping keys

    - #### getComparer

          public ItemOrderComparer getComparer​(SortKeyDefinitionList sKeys,
                                               AtomicComparer[] comps)

    - #### copy

          public Expression copy​(RebindingMap rebindings)

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Parameters:
        `rebindings` - variables that need to be re-bound
      Returns:
        the copy of the original expression

    - #### export

          public void export​(ExpressionPresenter out)
                      throws XPathException

      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
        `export` in interface `ExportAgent`
      Specified by:
        `export` in class `Expression`
      Parameters:
        `out` - the expression presenter used to display the structure
      Throws:
        `XPathException` - if the export fails, for example if an expression is found that won't work in the target environment.

    - #### processLeavingTail

          public TailCall processLeavingTail​(Outputter output,
                                             XPathContext context)
                                      throws XPathException

      Description copied from class: `Instruction`
      ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.
      Specified by:
        `processLeavingTail` in interface `TailCallReturner`
      Specified by:
        `processLeavingTail` in class `Instruction`
      Parameters:
        `output` - the destination for the result
        `context` - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
      Returns:
        null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
      Throws:
        `XPathException` - if a dynamic error occurs during the evaluation of the instruction

    - #### getStreamerName

          public java.lang.String getStreamerName()

      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
        `getStreamerName` in class `Expression`
      Returns:
        the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class