20 General utilities library [utilities]

20.14 Function objects [function.objects]

20.14.14 Function object binders [func.bind] Function template bind [func.bind.bind]

In the text that follows:
  • g is a value of the result of a bind invocation,
  • FD is the type decay_­t<F>,
  • 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),
  • is the type in the template parameter pack BoundArgs,
  • is the type decay_­t<>,
  • is the argument in the function parameter pack bound_­args,
  • is a bound argument entity of g ([func.def]) of type direct-non-list-initialized with std​::​forward<>(),
  • is the deduced type of the UnBoundArgs&&... parameter of the argument forwarding call wrapper, and
  • is the argument associated with .
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 in BoundArgs, is_­constructible_­v<, > is true.
Preconditions: FD and each meet the Cpp17MoveConstructible and Cpp17Destructible requirements.
INVOKE(fd, , , , ) ([func.require]) is a valid expression for some values , , , , where N has the value sizeof...(bound_­args).
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(, , , ) is expression-equivalent ([defns.expression-equivalent]) to
       static_cast<>(), static_cast<>(), , static_cast<>())
for the first overload, and
          static_cast<>(), static_cast<>(), , static_cast<>())
for the second overload, where the values and types of the target argument and of the bound arguments , , , are determined as specified below.
Throws: Any exception thrown by the initialization of the state entities of g.
If all of FD and meet the requirements of Cpp17CopyConstructible, then the return type meets the requirements of Cpp17CopyConstructible.
— end note
The values of the bound arguments , , , and their corresponding types , , , depend on the types derived from the call to bind and the cv-qualifiers cv of the call wrapper g as follows:
  • if is reference_­wrapper<T>, the argument is .get() and its type is T&;
  • if the value of is_­bind_­expression_­v<> is true, the argument is
    static_cast<cv &>()(std::forward<>()...)
    and its type is invoke_­result_­t<cv &, ...>&&;
  • if the value j of is_­placeholder_­v<> is not zero, the argument is std​::​forward<>() and its type is &&;
  • otherwise, the value is and its type is cv &.
The value of the target argument is fd and its corresponding type is cv FD&.