| Defined in header |
template <class F, class... Args> /*unspecified*/ bind_front( F&& f, Args&&... args );
The function template
bind_front generates a forwarding call wrapper for
f. Calling this wrapper is equivalent to invoking
f with its first
sizeof...(Args) parameters bound to
In other words,
std::bind_front(f, bound_args...)(call_args...) is equivalent to
std::invoke(f, bound_args..., call_args....).
The program is ill-formed if any of the following is not
(std::is_constructible_v<std::decay_t<Args>, Args> && ...)
(std::is_move_constructible_v<std::decay_t<Args>> && ...)
|f||-||Callable object (function object, pointer to function, reference to function, pointer to member function, or pointer to data member) that will be bound to some arguments|
|args||-|| list of the arguments to bind to the first
A function object of type
T that is unspecified, except that the types of objects returned by two calls to
std::bind_front with the same arguments are the same.
The returned object (call wrapper) has the following properties:
The returned object behaves as if it holds a member object
fd of type
std::decay_t<F> constructed from
std::forward<F>(f), and an
tup constructed with
std::make_tuple(std::forward<Args>(args)...) (this unwraps any
std::reference_wrappers), except that the returned object's assignment behavior is unspecified and the names are for exposition only.
The return type of
std::bind_front behaves as if its copy/move constructors perform a memberwise copy/move. It is CopyConstructible if all of its member objects (specified above) are CopyConstructible, and is MoveConstructible otherwise.
Given an object
G obtained from an earlier call to
bind_front(f, args...), when a glvalue
G is invoked in a function call expression
g(call_args...), an invocation of the stored object takes place, as if by.
std::invoke(g.fd, std::get<Ns>(g.tup)..., call_args...)
Nsis an integer pack
0, 1, ..., (sizeof...(Args) - 1)
gis an lvalue in the
std::invokeexpression if it is an lvalue in the call expression, and is an rvalue otherwise. Thus
std::move(g)(call_args...)can move the bound arguments into the call, where
The behavior is undefined if
g has volatile-qualified type.
The member operator() is noexcept if the
std::invoke expression it calls is noexcept (in other words, it preserves the exception specification of the underlying call operator).
Only throws if construction of stored function object or any of the bound arguments throws.
This function is intended to replace
std::bind. Unlike std::bind, it does not support arbitrary argument rearrangement and has no special treatment for nested bind-expressions. On the other hand, it pays attention to the value category of the call wrapper object and propagates exception specification of the underlying call operator.
As described in
std::invoke, when invoking a pointer to non-static member function or pointer to non-static data member, the first argument has to be a reference or pointer (including, possibly, smart pointer such as
std::unique_ptr) to an object whose member will be accessed.
| binds one or more arguments to a function object
| creates a function object out of a pointer to a member
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