value-type-binding.hpp File Reference

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Description

Type re-binding helper template for custom containers and adapters.

This header defines trait templates which are used by the Iterator adapters and similar custom containers to figure out the value-, pointer- and reference types when wrapping iterators or containers.

When writing a generic container or adapter, there is typically a point where you'll need some variation of the payload type: you may want to expose a reference, or you might need a pointer to the type, to implement a forwarding operator->(). On a technical level, this turns out surprisingly tricky, since we often don't know the exact "incantation" of the payload type and might thus end up forming a pointer to a rvalue reference or likewise illegal constructs.

Within the STL, there is a convention to provide nested typedefs to indicate type variations in relation to the basic payload type of the container. We follow this convention and support especially the

• value_type (what is conceived to be "in" the container or iterator)
• a simple (LValue) reference to the payload
• a pointer at the payload.

A custom container should likewise provide such type definitions, and the type rebinding helper template defined in this header makes it easy to provide such nested type definitions in a flexible way. This usage also creates an Extension Point: when some payload type requires special treatment, an explicit specialisation to this rebinding trait may be injected alongside with the definition of the payload type.

The CommonResultYield type rebinding helper allows to reconcile several essentially compatible result types; it is used in iterator pipelines, especially for the case of child expansion, where some additional sub-sequences are to be integrated into a main sequence.

See also

ValueTypeBinding_test

iter-adapter.hpp

scope-path.hpp usage example (explicit specialisation)

Definition in file value-type-binding.hpp.

#include "lib/error.hpp"
#include "lib/meta/trait.hpp"

Classes
struct	CommonResultYield< T1, T2, bool >
	Decision helper to select between returning results by value or reference. More...
struct	CommonResultYield< T1, T2, true >
class	has_nested_ValueTypeBindings< TY >
struct	has_nested_ValueTypeBindings< TY >::Probe< X, XX, XY, XZ >
struct	use_ValueTypebindings< X >
struct	ValueTypeBinding< TY, SEL >
	Type re-binding helper template for creating nested typedefs usable by custom containers and iterator adapters or similar. More...
struct	ValueTypeBinding< TY, enable_if< use_ValueTypebindings< TY > > >
	specialisation for classes providing STL style type binding definitions More...

Namespaces
	lib
	Implementation namespace for support and library code.

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Class Documentation

lib::meta::anonymous_namespace{value-type-binding.hpp}::has_nested_ValueTypeBindings::Probe

struct lib::meta::anonymous_namespace{value-type-binding.hpp}::has_nested_ValueTypeBindings::Probe

Collaboration diagram for has_nested_ValueTypeBindings< TY >::Probe< X, XX, XY, XZ >: