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Editor: | Google, Inc. |
Note: this is an early draft. It’s known to be incomplet and incorrekt, and it has lots of bad formatting.
This technical specification describes extensions to the C++
Standard Library (
This technical specification is non-normative. Some of the library components in this technical specification may be considered for standardization in a future version of C++, but they are not currently part of any C++ standard. Some of the components in this technical specification may never be standardized, and others may be standardized in a substantially changed form.
The goal of this technical specification is to build more widespread existing practice for an expanded C++ standard library. It gives advice on extensions to those vendors who wish to provide them.
The following referenced document is indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/IEC 14882:— is herein called the C++ Standard. References to clauses within the C++ Standard are written as "C++14 §3.2". The library described in ISO/IEC 14882:— clauses 17–30 is herein called the C++ Standard Library.
Unless otherwise specified, the whole of the C++ Standard's Library
introduction (
Since the extensions described in this technical specification
are experimental and not part of the C++ standard library, they
should not be declared directly within namespace
std
.
Unless otherwise specified, all components described in this technical specification either:
::experimental::fundamentals_v2
to a namespace defined in the C++ Standard Library,
such as std
or std::chrono
, or
std
.
std::experimental::fundamentals_v2::chrono
because the C++ Standard Library defines std::chrono
.
This TS does not define std::pmr::experimental::fundamentals_v2
because the C++ Standard Library does not define std::pmr
.
— end example ]
Each header described in this technical
specification shall import the contents of
std::experimental::fundamentals_v2
into
std::experimental
as if by
namespace std {
namespace experimental {
inline namespace fundamentals_v2 {}
}
}
Unless otherwise specified, references to other entities
described in this technical specification are assumed to be
qualified with std::experimental::fundamentals_v2::
,
and references to entities described in the standard are assumed
to be qualified with std::
.
Extensions that are expected to eventually be added to an
existing header <meow>
are provided inside the
<experimental/meow>
header, which shall include
the standard contents of <meow>
as if by
#include <meow>
New headers are also provided in the
<experimental/>
directory, but without such an
#include
.
|
This section describes tentative plans for future versions of this technical specification and plans for moving content into future versions of the C++ Standard.
The C++ committee intends to release a new version of this
technical specification approximately every year, containing the
library extensions we hope to add to a near-future version of the
C++ Standard. Future versions will define their contents in
std::experimental::fundamentals_v3
,
std::experimental::fundamentals_v4
, etc., with the
most recent implemented version inlined into
std::experimental
.
When an extension defined in this or a future version of this
technical specification represents enough existing practice, it
will be moved into the next version of the C++ Standard by
removing the experimental::fundamentals_vN
segment of its namespace and by removing the
experimental/
prefix from its header's path.
For the sake of improved portability between partial implementations of various C++ standards,
WG21 (the ISO technical committee for the C++ programming language) recommends
that implementers and programmers follow the guidelines in this section concerning feature-test macros.
Implementers who provide a new standard feature should define a macro with the recommended name,
in the same circumstances under which the feature is available (for example, taking into account relevant command-line options),
to indicate the presence of support for that feature.
Implementers should define that macro with the value specified in
the most recent version of this technical specification that they have implemented.
The recommended macro name is "__cpp_lib_experimental_
" followed by the string in the "Macro Name Suffix" column.
Programmers who wish to determine whether a feature is available in an implementation should base that determination on
the presence of the header (determined with __has_include(<header/name>)
) and
the state of the macro with the recommended name.
(The absence of a tested feature may result in a program with decreased functionality, or the relevant functionality may be provided in a different way.
A program that strictly depends on support for a feature can just try to use the feature unconditionally;
presumably, on an implementation lacking necessary support, translation will fail.)
Doc. No. | Title | Primary Section | Macro Name Suffix | Value | Header |
---|---|---|---|---|---|
N4076 | A proposal to add a generalized callable negator | not_fn
| 201406 | <experimental/functional>
|
<experimental/functional>
synopsis#include <functional>
namespace std {
namespace experimental {
inline namespace fundamentals_v2 {
// 2.2, Function template not_fn
template <class F> unspecified not_fn(F&& f);
} // namespace fundamentals_v2
} // namespace experimental
} // namespace std
not_fn
template <class F> unspecified not_fn(F&& f);
In the text that follows:
FD
is the type decay_t<F>
,fd
is an lvalue of type FD
constructed from std::forward<F>(f),
fn
is a forwarding call wrapper created as a result of not_fn(f)
,is_constructible<FD, F>::value
shall be true
.
fd
shall be a callable object (fn
such that the expression fn(a1, a2, ..., aN)
is equivalent to !INVOKE(fd, a1, a2, ..., aN)
(fd
throws an exception.MoveConstructible
.
If FD
satisfies the requirements of CopyConstructible
, then
the return type shall satisfy the requirements of CopyConstructible
.
FD
is MoveConstructible.
— end note ]
not_fn
can usually provide a better solution than using the negators not1
and not2
— end note ]