Provide a metafunction for substitutability of type references.
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Detailed Description
- Outline
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- Purpose:
- Provide a metafunction for substitutability of type references.
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- Classes:
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- See also:
- Component bslstl_function, bdef_function
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- Description:
- This private, subordinate component to
bslstl_function provides a Boolean metafunction, bslstl::Function_IsReferenceCompatible, which allows generic code to determine whether a reference to the first template parameter type (FROM_TYPE) can be substituted for a reference to the second template parameter type (TO_TYPE) with no loss of information. By default, this metafunction yields true_type if FROM_TYPE is the same as TO_TYPE; else it yields false_type. However, this template can be specialized to yield true_type for other parameters that have compatible references. In practice, this metafunction is used to detect types, such as bdef_Function, that convert to bsl::function and wrap it with no additional data members; bslstl::Function_IsReferenceCompatible would be specialized to yield true_type for such wrapper types. This metafunction is used within an enable_if to prevent types that are reference compatible with bsl::function from matching template parameters in function constructors and assignment operators, preferring, instead, the non-template overloads for copy and move construction and assignment. Note that reference qualifiers on FROM_TYPE and TO_TYPE will cause instantiation to fail; the caller should strip reference qualifiers on FROM_TYPE and TO_TYPE before checking for reference compatibility. This component exists solely to provide a transition from bdef_Function to bsl::function so that the former can eventually be deprecated and removed. This component should therefore also be considered deprecated and will be removed when bdef_Function is removed.
