20 General utilities library [utilities]

In the text that follows:

• (1.1)
  g is a value of the result of a bind_­front invocation,
• (1.2)
  FD is the type decay_­t<F>,
• (1.3)
  fd is the target object of g ([func.def]) of type FD, direct-non-list-initialized with std​::​forward<F​>(f),
• (1.4)
  BoundArgs is a pack that denotes decay_­t<Args>...,
• (1.5)
  bound_­args is a pack of bound argument entities of g ([func.def]) of types BoundArgs..., direct-non-list-initialized with std​::​forward<Args>(args)..., respectively, and
• (1.6)
  call_­args is an argument pack used in a function call expression ([expr.call]) of g.

Mandates:

is_constructible_v<FD, F> &&
is_move_constructible_v<FD> &&
(is_constructible_v<BoundArgs, Args> && ...) &&
(is_move_constructible_v<BoundArgs> && ...)

is true.

Preconditions: FD meets the Cpp17MoveConstructible requirements.

For each ${\text{T}}_i$ in BoundArgs, if ${\text{T}}_i$ is an object type, ${\text{T}}_i$ meets the Cpp17MoveConstructible requirements.

Returns: A perfect forwarding call wrapper g with call pattern invoke(fd, bound_­args..., call_­args...).

Throws: Any exception thrown by the initialization of the state entities of g ([func.def]).