Package net.sf.saxon.expr
Class LookupExpression
- java.lang.Object
-
- net.sf.saxon.expr.Expression
-
- net.sf.saxon.expr.BinaryExpression
-
- net.sf.saxon.expr.LookupExpression
-
- All Implemented Interfaces:
ExportAgent,Locatable,IdentityComparable,Traceable
- Direct Known Subclasses:
ObjectLookupExpression
public class LookupExpression extends BinaryExpression
A lookup expression is an expression of the form A?B. Here A must be a sequence of maps or arrays. In the general case B is an expression that computes a key/index into the map or array; the case where B is constant needs to be handled efficiently. The class also implements the unary lookup expression ?B, which is interpreted as .?B. It does not handle the case A?* - that is handled as a LookupAllExpression.
-
-
Field Summary
Fields Modifier and Type Field Description protected booleanisArrayLookupprotected booleanisMapLookupprotected booleanisSingleContainerprotected booleanisSingleEntry-
Fields inherited from class net.sf.saxon.expr.BinaryExpression
operator
-
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 LookupExpression(Expression start, Expression step)Constructor
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description intcomputeCardinality()Determine the static cardinality of the expressionintcomputeHashCode()get HashCode for comparing two expressionsLookupExpressioncopy(RebindingMap rebindings)Copy an expression.booleanequals(java.lang.Object other)Is this expression the same as another expression?voidexport(ExpressionPresenter destination)Diagnostic print of expression structure.doublegetCost()Return the estimated cost of evaluating an expression.java.lang.StringgetExpressionName()Get a name identifying the kind of expression, in terms meaningful to a user.intgetImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().ItemTypegetItemType()Determine the data type of the items returned by this expressionprotected OperandRolegetOperandRole(int arg)Get the operand roleUTypegetStaticUType(UType contextItemType)Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.SequenceIteratoriterate(XPathContext context)Iterate the lookup-expression in a given contextprotected static voidmustBeArrayOrMap(Expression exp, Item baseItem)Expressionoptimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)Perform optimisation of an expression and its subexpressions.java.lang.StringtoString()The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.ExpressiontypeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)Type-check the expression-
Methods inherited from class net.sf.saxon.expr.BinaryExpression
computeSpecialProperties, displayOperator, explainExtraAttributes, getLhs, getLhsExpression, getOperator, getRhs, getRhsExpression, isAssociative, isCommutative, isInverse, operands, setFlattened, setLhsExpression, setRhsExpression, tag, toShortString
-
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStreamerName, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, 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
-
-
-
-
Constructor Detail
-
LookupExpression
public LookupExpression(Expression start, Expression step)
Constructor- Parameters:
start- The left hand operand (which must always select a sequence of maps or arrays).step- The step to be followed from each map/array in the start expression to yield a new sequence
-
-
Method Detail
-
getOperandRole
protected OperandRole getOperandRole(int arg)
Description copied from class:BinaryExpressionGet the operand role- Overrides:
getOperandRolein classBinaryExpression- Parameters:
arg- which argument: 0 for the lhs, 1 for the rhs- Returns:
- the operand role
-
getExpressionName
public java.lang.String getExpressionName()
Description copied from class:ExpressionGet a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionNamein classExpression- Returns:
- a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.
-
getItemType
public ItemType getItemType()
Determine the data type of the items returned by this expression- Specified by:
getItemTypein classExpression- Returns:
- the type of the expression, as far as this is known. Prior to type-checking,
the method returns
AnyItemType
-
getStaticUType
public UType getStaticUType(UType contextItemType)
Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.- Overrides:
getStaticUTypein classExpression- Parameters:
contextItemType- not used- Returns:
- the static item type of the expression according to the XSLT 3.0 defined rules
-
typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
Type-check the expression- Overrides:
typeCheckin classBinaryExpression- Parameters:
visitor- an expression visitorcontextInfo- 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)
-
optimize
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
Description copied from class:BinaryExpressionPerform 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.
- Overrides:
optimizein classBinaryExpression- Parameters:
visitor- an expression visitorcontextInfo- 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 toType.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)
-
getCost
public double getCost()
Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.- Overrides:
getCostin classExpression- Returns:
- a rough estimate of the cost of evaluation
-
getImplementationMethod
public int getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.- Overrides:
getImplementationMethodin classBinaryExpression- Returns:
- the implementation method, for example
Expression.ITERATE_METHODorExpression.EVALUATE_METHODorExpression.PROCESS_METHOD
-
copy
public LookupExpression copy(RebindingMap rebindings)
Copy an expression. This makes a deep copy.- Specified by:
copyin classExpression- Parameters:
rebindings- a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.- Returns:
- the copy of the original expression
-
computeCardinality
public int computeCardinality()
Determine the static cardinality of the expression- Overrides:
computeCardinalityin classBinaryExpression- Returns:
- the computed cardinality, as one of the values
StaticProperty.ALLOWS_ZERO_OR_ONE,StaticProperty.EXACTLY_ONE,StaticProperty.ALLOWS_ONE_OR_MORE,StaticProperty.ALLOWS_ZERO_OR_MORE. May also returnStaticProperty.ALLOWS_ZEROif the result is known to be an empty sequence, orStaticProperty.ALLOWS_MANYif if is known to return a sequence of length two or more.
-
equals
public boolean equals(java.lang.Object other)
Is this expression the same as another expression?- Overrides:
equalsin classBinaryExpression- Parameters:
other- the other operand; the result is false if this is not an Expression- Returns:
- true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.
-
computeHashCode
public int computeHashCode()
get HashCode for comparing two expressions- Overrides:
computeHashCodein classBinaryExpression- Returns:
- a computed hash code
-
iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Iterate the lookup-expression in a given context- Overrides:
iteratein classExpression- Parameters:
context- the evaluation context- 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
-
mustBeArrayOrMap
protected static void mustBeArrayOrMap(Expression exp, Item baseItem) throws XPathException
- Throws:
XPathException
-
export
public void export(ExpressionPresenter destination) throws XPathException
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
exportin interfaceExportAgent- Overrides:
exportin classBinaryExpression- Parameters:
destination- the output destination for the displayed expression tree- Throws:
XPathException- if the export fails, for example if an expression is found that won't work in the target environment.
-
toString
public java.lang.String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax- Overrides:
toStringin classBinaryExpression- Returns:
- a representation of the expression as a string
-
-