Qt 4.8
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Creates a DynamicContext which provides the focus item for the function fn:current()
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#include <qcurrentitemstore_p.h>
Private Functions | |
DynamicContext::Ptr | createContext (const DynamicContext::Ptr &old) const |
Static Private Functions | |
static StaticContext::Ptr | newStaticContext (const StaticContext::Ptr &context) |
Creates a DynamicContext which provides the focus item for the function fn:current()
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Definition at line 71 of file qcurrentitemstore_p.h.
CurrentItemStore::CurrentItemStore | ( | const Expression::Ptr & | operand | ) |
Definition at line 53 of file qcurrentitemstore.cpp.
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Implements QPatternist::Expression.
Definition at line 124 of file qcurrentitemstore.cpp.
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Returns this
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Reimplemented from QPatternist::Expression.
Definition at line 129 of file qcurrentitemstore.cpp.
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compress() is the last stage performs in compiling an expression, done after the initial AST build and calling typeCheck(). compress() performs crucial simplifications, either by having drastic performance implications or that some expressions depend on it for proper behavior.
The default implementation performs a sparse conditional constant propagation. In short, a recursive process is performed in the AST which examines if the Expression's operands are constant values, and if so, performs a const fold(AST rewrite) into the result of evaluating the expression in question. This default behavior can be disabled by letting properties() return DisableElimination.
This compress() stage can be relative effective due to the design of XPath, in part because intrinsic functions are heavily used. Many Expressions override compress() and do optimizations specific to what they do. Also, many Expressions performs optimizations in their typeCheck().
context | the static context. Supplies compile time information, and is the channel for communicating error messages. |
Reimplemented from QPatternist::Expression.
Definition at line 101 of file qcurrentitemstore.cpp.
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Definition at line 57 of file qcurrentitemstore.cpp.
Referenced by evaluateEBV(), evaluateSequence(), and evaluateSingleton().
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Determines the Effective Boolean Value of the expression.
The Effective Boolean Value of a value is not necessarily the same as converting the value to a new value of type xs:boolean.
Note that this function cannot return the empty sequence, evaluateSingleton() must be overridden in order to be able to do that.
The default implementation results in a type error. Hence, this function must be overridden if such behavior is not of interest.
Reimplemented from QPatternist::Expression.
Definition at line 62 of file qcurrentitemstore.cpp.
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Evaluate this Expression by iterating over it. This is a central function for evaluating expressions.
Expressions must always always return a valid QAbstractXmlForwardIterator and may never return 0. If an empty result is of interest to be returned, the EmptyIterator should be returned.
The default implementation returns a SingletonIterator over the item returned from evaluateSingleton().
Reimplemented from QPatternist::Expression.
Definition at line 67 of file qcurrentitemstore.cpp.
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Reimplemented from QPatternist::Expression.
Definition at line 72 of file qcurrentitemstore.cpp.
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Returns a list of Sequence Types, describing the type of each of the expression's operands. Hence, this function has a relationship to the operands() function:
- The lengths of the lists returned by expectedOperandTypes() and operands() should always be equal in length, since one cannot describe the type of a non-existent operand(and all operands must have type information). - A significant difference between the two functions is that while the type of objects in the list returned by operands() may vary between compilations/static context, simply because the particular Expression is part of different XPath expressions, the types in the list returned by expectedOperandTypes is always the same since the function/operator signature never changes.
This function should not be confused with staticType(), which returns the static type of the expression itself, not its operands. The function call is an expression where this is clear: the type of the return value is not the same as the arguments' types. The static type of the operands supplied to the expression can be determined via the staticType() function of the instances returned by operands().
If the expression has no operands, an empty list should be returned.
Implements QPatternist::Expression.
Definition at line 82 of file qcurrentitemstore.cpp.
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inlinestaticprivate |
Definition at line 89 of file qcurrentitemstore.cpp.
Referenced by compress(), and typeCheck().
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The default implementation returns 0. Override and let the function return a different value, if that's of interest.
An important decision when re-implementing properties() is whether to OR in the properties() of ones operands. For instance, if an operand has RequiresFocus set, that flag nost likely applies to the apparent as well, since it depends on its operand.
Reimplemented from QPatternist::Expression.
Definition at line 134 of file qcurrentitemstore.cpp.
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Implements QPatternist::Expression.
Definition at line 77 of file qcurrentitemstore.cpp.
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This implementation guarantees to never rewrite away this Expression, but at most rewrite it as a child of another expression(that presumably have a type checking role). It is therefore always safe to override this function and call this implementation and not worry about that this Expression becomes deleted.
Many Expressions override typeCheck() and performs optimizations, as opposed to doing it in the compress() stage. This is due to that the design of those Expressions often are tied to that certain simplifications are done at the typeCheck() stage of the compilation process or that it in some other way is related to what the typeCheck() do. Also, the earlier the AST can be simplified, the better the chances are for subsequent optimizations.
It is important that the super class's typeCheck() is called before doing any custom type checking, since the call can change the children(notably, the childrens' static types). For example, if the Expression, MyExpression in the example, does not match the required type, typeCheck returns the Expression wrapped in for example ItemVerifier, CardinalityVerifier, or both.
typeCheck() may be called many times. typeCheck() must either raise an error if this Expression is an invalid expression. Thus, it is guaranteed that an Expression is valid after typeCheck() is called.
context | supplies information, such as namespace bindings and available function signatures, that can be needed at compilation time. context is guaranteed by the caller to never null. |
reqType | the static type that this Expression must match when evaluated. reqType is guaranteed by the caller to never null. |
reqType
Reimplemented from QPatternist::Expression.
Definition at line 118 of file qcurrentitemstore.cpp.