net.sf.saxon.expr

Class Atomizer

public final class Atomizer extends UnaryExpression implements DivisibleInstruction

An Atomizer is an expression corresponding essentially to the fn:data() function: it maps a sequence by replacing nodes with their typed values
Nested Class Summary
static classAtomizer.AtomizingFunction
Implement the mapping function.
Constructor Summary
Atomizer(Expression sequence)
Constructor
Method Summary
PathMap.PathMapNodeSetaddToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
intcomputeCardinality()
Determine the static cardinality of the expression
intcomputeSpecialProperties()
Determine the special properties of this expression
Expressioncopy()
Copy an expression.
StringdisplayExpressionName()
Diagnostic print of expression structure.
ItemevaluateItem(XPathContext context)
Evaluate as an Item.
static ItemTypegetAtomizedItemType(Expression operand, boolean alwaysUntyped, TypeHierarchy th)
Compute the type that will result from atomizing the result of a given expression
static SequenceIteratorgetAtomizingIterator(SequenceIterator base)
Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible
SequenceIteratoriterate(XPathContext context)
Iterate over the sequence of values
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
voidprocess(XPathContext context)
Process the instruction, without returning any tail calls
voidprocessLeft(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the first half of the instruction (for example, to start a new document or element)
voidprocessRight(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the right half of the instruction (for example, to end a new document or element) Note that unlike other divisible instructions this one doesn't push the result to the current output destination, it leaves a sequenceIterator over the result on the stack.
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Constructor Detail

Atomizer

public Atomizer(Expression sequence)
Constructor

Parameters: sequence the sequence to be atomized

Method Detail

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Parameters: pathMap the PathMap to which the expression should be added pathMapNodeSet the PathMapNodeSet to which the paths embodied in this expression should be added

Returns: the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

computeCardinality

public int computeCardinality()
Determine the static cardinality of the expression

computeSpecialProperties

public int computeSpecialProperties()
Determine the special properties of this expression

Returns: NON_CREATIVE.

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

displayExpressionName

public String displayExpressionName()
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

evaluateItem

public Item evaluateItem(XPathContext context)
Evaluate as an Item. This should only be called if the Atomizer has cardinality zero-or-one, which will only be the case if the underlying expression has cardinality zero-or-one.

getAtomizedItemType

public static ItemType getAtomizedItemType(Expression operand, boolean alwaysUntyped, TypeHierarchy th)
Compute the type that will result from atomizing the result of a given expression

Parameters: operand the given expression alwaysUntyped true if it is known that nodes will always be untyped th the type hierarchy cache

Returns: the item type of the result of evaluating the operand expression, after atomization

getAtomizingIterator

public static SequenceIterator getAtomizingIterator(SequenceIterator base)
Get an iterator that returns the result of atomizing the sequence delivered by the supplied iterator

Parameters: base the supplied iterator, the input to atomization

Returns: an iterator that returns atomic values, the result of the atomization

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible

Parameters: th the type hierarchy cache

Returns: a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER. For this class, the result is always an atomic type, but it might be more specific.

iterate

public SequenceIterator iterate(XPathContext context)
Iterate over the sequence of values

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.

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.

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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

Throws: net.sf.saxon.trans.XPathException if an error is discovered during this phase (typically a type error)

process

public void process(XPathContext context)
Process the instruction, without returning any tail calls

Parameters: context The dynamic context, giving access to the current node, the current variables, etc.

processLeft

public void processLeft(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the first half of the instruction (for example, to start a new document or element)

Parameters: contextStack state a stack on which the instruction can save state information during the call on processLeft()

processRight

public void processRight(Stack<XPathContext> contextStack, Stack state)
In streaming mode, process the right half of the instruction (for example, to end a new document or element) Note that unlike other divisible instructions this one doesn't push the result to the current output destination, it leaves a sequenceIterator over the result on the stack.

Parameters: contextStack state a stack on which the instruction can save state information during the call on processLeft()

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Parameters: visitor an expression visitor

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression