[func.bind]

The class template is_bind_expression can be used to detect function objects generated by bind.

The function template bind uses is_bind_expression to detect subexpressions.

Specializations of the is_bind_expression template shall meet the Cpp17UnaryTypeTrait requirements ([meta.rqmts]).

The implementation provides a definition that has a base characteristic of true_type if T is a type returned from bind, otherwise it has a base characteristic of false_type.

A program may specialize this template for a program-defined type T to have a base characteristic of true_type to indicate that T should be treated as a subexpression in a bind call.

22.10.15.3 Class template is_placeholder [func.bind.isplace]

🔗

namespace std { template<class T> struct is_placeholder; / see below }

The class template is_placeholder can be used to detect the standard placeholders _1, _2, and so on ([func.bind.place]).

The function template bind uses is_placeholder to detect placeholders.

Specializations of the is_placeholder template shall meet the Cpp17UnaryTypeTrait requirements ([meta.rqmts]).

The implementation provides a definition that has the base characteristic of integral_constant<int, J> if T is the type of std::placeholders::_J, otherwise it has a base characteristic of integral_constant<int, 0>.

A program may specialize this template for a program-defined type T to have a base characteristic of integral_constant<int, N> with N > 0 to indicate that T should be treated as a placeholder type.

22.10.15.4 Function template bind [func.bind.bind]

In the text that follows:

(1.1)
g is a value of the result of a bind invocation,
(1.2)
FD is the type decay_t<F>,
(1.3)
fd is an lvalue that is a target object of g ([func.def]) of type FD direct-non-list-initialized with std::forward<F>(f),
(1.4)
$T {i is the {i th type in the template parameter pack BoundArgs,}^{th type in the template parameter pack BoundArgs,}}_{i is the {i th type in the template parameter pack BoundArgs,}^{th type in the template parameter pack BoundArgs,}}$
(1.5)
$TD {i is the type decay_t < T {i >,}_{i >}}_{i is the type decay_t < T {i >,}_{i >}}$
(1.6)
$t {i is the {i th argument in the function parameter pack bound_args,}^{th argument in the function parameter pack bound_args,}}_{i is the {i th argument in the function parameter pack bound_args,}^{th argument in the function parameter pack bound_args,}}$
(1.7)
$td {i is a bound argument entity of g ([func. def]) of type TD {i direct-non-list-initialized with std :: forward < T {i > (t {i),}_{i)}}_{i > (t {i),}_{i)}}}_{i direct-non-list-initialized with std :: forward < T {i > (t {i),}_{i)}}_{i > (t {i),}_{i)}}}}_{i is a bound argument entity of g ([func. def]) of type TD {i direct-non-list-initialized with std :: forward < T {i > (t {i),}_{i)}}_{i > (t {i),}_{i)}}}_{i direct-non-list-initialized with std :: forward < T {i > (t {i),}_{i)}}_{i > (t {i),}_{i)}}}}$
(1.8)
$U {j is the {j th deduced type of the UnBoundArgs & & . parameter of the argument forwarding call wrapper, and}^{th deduced type of the UnBoundArgs & & . parameter of the argument forwarding call wrapper, and}}_{j is the {j th deduced type of the UnBoundArgs & & . parameter of the argument forwarding call wrapper, and}^{th deduced type of the UnBoundArgs & & . parameter of the argument forwarding call wrapper, and}}$
(1.9)
$u {j is the {j th argument associated with U {j .}_{j .}}^{th argument associated with U {j .}_{j .}}}_{j is the {j th argument associated with U {j .}_{j .}}^{th argument associated with U {j .}_{j .}}}$

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template<class F, class. BoundArgs>
  constexpr unspecified bind(F&& f, BoundArgs&&. bound_args);
template<class R, class F, class. BoundArgs>
  constexpr unspecified bind(F&& f, BoundArgs&&. bound_args);

Mandates: is_constructible_v<FD, F> is true.

For each

T {i in BoundArgs, is_constructible_v < TD {i, T {i > is true .}_{i >}}_{i, T {i > is true .}_{i >}}}_{i in BoundArgs, is_constructible_v < TD {i, T {i > is true .}_{i >}}_{i, T {i > is true .}_{i >}}}

Preconditions: FD and each

TD {i meet the Cpp17MoveConstructible and Cpp17Destructible requirements .}_{i meet the Cpp17MoveConstructible and Cpp17Destructible requirements .}

INVOKE(fd,

w {1, w {2, \dots, w {N) ([func. require]) is a valid expression for some values w {1, w {2, \dots, w_{, where has the value}}_{2, \dots, w {, where has the value}_{, where has the value bound_args .}}}_{1, w {2, \dots, w {, where has the value}_{, where has the value bound_args .}}_{2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}}}_{N)}}_{2, \dots, w {N) ([func. require]) is a valid expression for some values w {1, w {2, \dots, w {, where has the value}_{, where has the value bound_args .}}_{2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}}_{1, w {2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}_{2, \dots, w {N, where N has the value sizeof . (bound_args) .}_{N, where N has the value sizeof . (bound_args) .}}}}_{N)}}}_{1, w {2, \dots, w {N) ([func. require]) is a valid expression for some values w {1, w {2, \dots, w {, where has the value}_{, where has the value bound_args .}}_{2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}}_{1, w {2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}_{2, \dots, w {N, where N has the value sizeof . (bound_args) .}_{N, where N has the value sizeof . (bound_args) .}}}}_{N)}}_{2, \dots, w {N) ([func. require]) is a valid expression for some values w {1, w {2, \dots, w {, where has the value bound_args .}_{N, where N has the value sizeof . (bound_args) .}}_{2, \dots, w {N, where N has the value sizeof . (bound_args) .}_{N, where N has the value sizeof . (bound_args) .}}}_{1, w {2, \dots, w {N, where N has the value sizeof . (bound_args) .}_{N, where N has the value sizeof . (bound_args) .}}_{2, \dots, w {N, where N has the value sizeof . (bound_args) .}_{N, where N has the value sizeof . (bound_args) .}}}}_{N)}}}

Returns: An argument forwarding call wrapper g ([func.require]).

A program that attempts to invoke a volatile-qualified g is ill-formed.

When g is not volatile-qualified, invocation of g(

u {1, u {2, \dots, u {M) is expression-equivalent ([defns. expression. equivalent]) to INVOKE (static_cast < V {fd > (v {fd), static_cast <}_{fd), static_cast <}}_{fd > (v {fd), static_cast <}_{fd), static_cast <}}}_{M)}}_{2, \dots, u {M) is expression-equivalent ([defns. expression. equivalent]) to INVOKE (static_cast < V {fd > (v {fd), static_cast <}_{fd), static_cast <}}_{fd > (v {fd), static_cast <}_{fd), static_cast <}}}_{M)}}}_{1, u {2, \dots, u {M) is expression-equivalent ([defns. expression. equivalent]) to INVOKE (static_cast < V {fd > (v {fd), static_cast <}_{fd), static_cast <}}_{fd > (v {fd), static_cast <}_{fd), static_cast <}}}_{M)}}_{2, \dots, u {M) is expression-equivalent ([defns. expression. equivalent]) to INVOKE (static_cast < V {fd > (v {fd), static_cast <}_{fd), static_cast <}}_{fd > (v {fd), static_cast <}_{fd), static_cast <}}}_{M)}}}

Throws: Any exception thrown by the initialization of the state entities of g.

[Note 1:

If all of FD and

TD {i meet the requirements of Cpp17CopyConstructible, then the return type meets the requirements of Cpp17CopyConstructible .}_{i meet the requirements of Cpp17CopyConstructible, then the return type meets the requirements of Cpp17CopyConstructible .}

— end note]

The values of the bound arguments

The value of the target argument

v {fd is fd and its corresponding type V {fd is cv FD & .}_{fd is cv FD & .}}_{fd is fd and its corresponding type V {fd is cv FD & .}_{fd is cv FD & .}}

22.10.15.5 Placeholders [func.bind.place]

namespace std::placeholders { / M is the number of placeholders see below _1; see below _2; ⋮ see below _M; }

The number M of placeholders is implementation-defined.

All placeholder types meet the Cpp17DefaultConstructible and Cpp17CopyConstructible requirements, and their default constructors and copy/move constructors are constexpr functions that do not throw exceptions.

It is implementation-defined whether placeholder types meet the Cpp17CopyAssignable requirements, but if so, their copy assignment operators are constexpr functions that do not throw exceptions.

Placeholders should be defined as: inline constexpr unspecified _1{};

If they are not, they are declared as: extern unspecified _1;

Placeholders are freestanding items ([freestanding.item]).

22.10.15.2 Class template is_bind_expression [func.bind.isbind]

22.10.15.3 Class template is_placeholder [func.bind.isplace]

22.10.15.4 Function template bind [func.bind.bind]

22.10.15.5 Placeholders [func.bind.place]