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## net.sf.saxon.expr
Class Optimizer

    java.lang.Object
      net.sf.saxon.expr.Optimizer

All Implemented Interfaces:
  java.io.Serializable

Direct Known Subclasses:
  OptimizerSA

    public class Optimizer

extends java.lang.Object
implements java.io.Serializable

This class performs optimizations that vary between different versions of the Saxon product. The optimizer is obtained from the Saxon Configuration. This class is the version used in Saxon-B, which in most cases does no optimization at all: the methods are provided so that they can be overridden in Saxon-SA.

See Also:
  Serialized Form

Field Summary
`protected Configuration` | `config`

Constructor Summary
`Optimizer(Configuration config)` Create an Optimizer.

Method Summary
`Expression` | `convertPathExpressionToKey(PathExpression pathExp, ExpressionVisitor visitor)` Examine a path expression to see whether it can be replaced by a call on the key() function; if so, generate an appropriate key definition and return the call on key().
`FilterExpression` | `convertToFilterExpression(PathExpression pathExp, TypeHierarchy th)` Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate].
`Expression` | `extractGlobalVariables(Expression body, ExpressionVisitor visitor)` Extract subexpressions from the body of a function that can be evaluated as global variables
`Configuration` | `getConfiguration()` Get the Saxon configuration object
`int` | `isIndexableFilter(Expression filter)` Test whether a filter predicate is indexable.
`Value` | `makeClosure(Expression expression, int ref, XPathContext context)` Make a Closure, given the expected reference count
`Expression` | `makeConditionalDocumentSorter(DocumentSorter sorter, PathExpression path)` Make a conditional document sorter.
`BinaryExpression` | `makeGeneralComparison(Expression p0, int op, Expression p1, boolean backwardsCompatible)` Create a GeneralComparison expression
`ValueRepresentation` | `makeIndexedValue(SequenceIterator iter)` Create an indexed value
`ValueRepresentation` | `makeSequenceExtent(Expression expression, int ref, XPathContext context)` Make a SequenceExtent, given the expected reference count
`Expression` | `optimizeCopy(Expression select)` Attempt to optimize a copy operation.
`Expression` | `promoteExpressionsToGlobal(Expression body, ExpressionVisitor visitor)` Identify expressions within a function or template body that can be promoted to be evaluated as global variables.
`void` | `trace(java.lang.String message)` Trace optimization actions
`void` | `trace(java.lang.String message, Expression exp)` Trace optimization actions
`Expression` | `tryIndexedFilter(FilterExpression f, ExpressionVisitor visitor, boolean indexFirstOperand)` Try converting a filter expression to a call on the key function.
`Expression` | `tryInlineFunctionCall(UserFunctionCall functionCall, ExpressionVisitor visitor, ItemType contextItemType)` Replace a function call by the body of the function, assuming all conditions for inlining the function are satisfied
`Expression` | `trySwitch(Choose choose, StaticContext env)` Try to convert a Choose expression into a switch

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

Field Detail

### config

    protected Configuration config

Constructor Detail

### Optimizer

    public Optimizer(Configuration config)

  Create an Optimizer.

  Parameters:
    `config` - the Saxon configuration

Method Detail

### getConfiguration

    public Configuration getConfiguration()

  Get the Saxon configuration object

  Returns:
    the configuration

### makeGeneralComparison

    public BinaryExpression makeGeneralComparison(Expression p0,
                                                  int op,
                                                  Expression p1,
                                                  boolean backwardsCompatible)

  Create a GeneralComparison expression

  Parameters:
    `p0` - the first operand
    `op` - the operator
    `p1` - the second operand
    `backwardsCompatible` - true if XPath 1.0 backwards compatibility is in force
  Returns:
    the constructed expression

### optimizeCopy

    public Expression optimizeCopy(Expression select)
                            throws XPathException

  Attempt to optimize a copy operation. Return null if no optimization is possible.

  Parameters:
    `select` - the expression that selects the items to be copied
  Returns:
    null if no optimization is possible, or an expression that does an optimized copy of these items otherwise
  Throws:
    `XPathException`

### makeClosure

    public Value makeClosure(Expression expression,
                             int ref,
                             XPathContext context)
                      throws XPathException

  Make a Closure, given the expected reference count

  Parameters:
    `expression` - the expression to be evaluated
    `ref` - the (nominal) number of times the value of the expression is required
    `context` - the XPath dynamic evaluation context
  Returns:
    the constructed Closure
  Throws:
    `XPathException`

### makeSequenceExtent

    public ValueRepresentation makeSequenceExtent(Expression expression,
                                                  int ref,
                                                  XPathContext context)
                                           throws XPathException

  Make a SequenceExtent, given the expected reference count

  Parameters:
    `expression` - the expression to be evaluated
    `ref` - the (nominal) number of times the value of the expression is required
    `context` - the XPath dynamic evaluation context
  Returns:
    the constructed Closure
  Throws:
    `XPathException`

### convertPathExpressionToKey

    public Expression convertPathExpressionToKey(PathExpression pathExp,
                                                 ExpressionVisitor visitor)
                                          throws XPathException

  Examine a path expression to see whether it can be replaced by a call on the key() function; if so, generate an appropriate key definition and return the call on key(). If not, return null.

  Parameters:
    `pathExp` - The path expression to be converted.
    `visitor` - The expression visitor
  Returns:
    the optimized expression, or null if no optimization is possible
  Throws:
    `XPathException`

### tryIndexedFilter

    public Expression tryIndexedFilter(FilterExpression f,
                                       ExpressionVisitor visitor,
                                       boolean indexFirstOperand)

  Try converting a filter expression to a call on the key function. Return the supplied expression unchanged if not possible

  Parameters:
    `f` - the filter expression to be converted
    `visitor` - the expression visitor, which must be currently visiting the filter expression f
    `indexFirstOperand` - true if the first operand of the filter comparison is to be indexed; false if it is the second operand
  Returns:
    the optimized expression, or the unchanged expression f if no optimization is possible

### convertToFilterExpression

    public FilterExpression convertToFilterExpression(PathExpression pathExp,
                                                      TypeHierarchy th)
                                               throws XPathException

  Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate]. This is possible whenever the predicate is non-positional. The conversion is useful in the case where the path expression appears inside a loop, where the predicate depends on the loop variable but a/b/c does not.

  Parameters:
    `pathExp` - the path expression to be converted
    `th` - the type hierarchy cache
  Returns:
    the resulting filterexpression if conversion is possible, or null if not
  Throws:
    `XPathException`

### isIndexableFilter

    public int isIndexableFilter(Expression filter)

  Test whether a filter predicate is indexable.

  Parameters:
    `filter` - the predicate expression
  Returns:
    0 if not indexable; +1 if the predicate is in the form expression=value; -1 if it is in the form value=expression

### makeIndexedValue

    public ValueRepresentation makeIndexedValue(SequenceIterator iter)
                                         throws XPathException

  Create an indexed value

  Parameters:
    `iter` - the iterator that delivers the sequence of values to be indexed
  Returns:
    the indexed value
  Throws:
    `UnsupportedOperationException:` - this method should not be called in Saxon-B
    `XPathException`

### makeConditionalDocumentSorter

    public Expression makeConditionalDocumentSorter(DocumentSorter sorter,
                                                    PathExpression path)

  Make a conditional document sorter. This optimization is attempted when a DocumentSorter is wrapped around a path expression

  Parameters:
    `sorter` - the document sorter
    `path` - the path expression
  Returns:
    the original sorter unchanged when no optimization is possible, which is always the case in Saxon-B

### tryInlineFunctionCall

    public Expression tryInlineFunctionCall(UserFunctionCall functionCall,
                                            ExpressionVisitor visitor,
                                            ItemType contextItemType)

  Replace a function call by the body of the function, assuming all conditions for inlining the function are satisfied

  Parameters:
    `functionCall` - the functionCall expression
    `visitor` - the expression visitor
    `contextItemType` - the context item type
  Returns:
    either the original expression unchanged, or an expression that consists of the inlined function body, with all function parameters bound as required. In Saxon-B, function inlining is not supported, so the original functionCall is always returned unchanged

### promoteExpressionsToGlobal

    public Expression promoteExpressionsToGlobal(Expression body,
                                                 ExpressionVisitor visitor)
                                          throws XPathException

  Identify expressions within a function or template body that can be promoted to be evaluated as global variables.

  Parameters:
    `body` - the body of the template or function
    `visitor` - the expression visitor
  Returns:
    the expression after subexpressions have been promoted to global variables
  Throws:
    `XPathException`

### trySwitch

    public Expression trySwitch(Choose choose,
                                StaticContext env)

  Try to convert a Choose expression into a switch

  Parameters:
    `choose` - the Choose expression
    `env` - the static context
  Returns:
    the result of optimizing this (the original expression if no optimization was possible)

### extractGlobalVariables

    public Expression extractGlobalVariables(Expression body,
                                             ExpressionVisitor visitor)
                                      throws XPathException

  Extract subexpressions from the body of a function that can be evaluated as global variables

  Parameters:
    `body` - the body of the function
  Returns:
    a reference to the new global variable if a variable has been created, or null if not
  Throws:
    `XPathException`

### trace

    public void trace(java.lang.String message,
                      Expression exp)

  Trace optimization actions

  Parameters:
    `message` - the message to be displayed
    `exp` - the expression after being rewritten

### trace

    public void trace(java.lang.String message)

  Trace optimization actions

  Parameters:
    `message` - the message to be displayed

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