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std::bind

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<tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody> <tbody class="t-dcl-rev t-dcl-rev-num "> </tbody><tbody> </tbody>
(1)
template< class F, class... Args > /* */ bind( F&& f, Args&&... args );
 ( C++11)
( C++20)
template< class F, class... Args > constexpr /* */ bind( F&& f, Args&&... args );
 ( C++20)
(2)
template< class R, class F, class... Args > /* */ bind( F&& f, Args&&... args );
 ( C++11)
( C++20)
template< class R, class F, class... Args > constexpr /* */ bind( F&& f, Args&&... args );
 ( C++20)

std::bind f. f , args.

std::is_constructible<std::decay<F>::type, F>::value false std::is_constructible<std::decay<Arg_i>::type, Arg_i>::value false Arg_i Args, .

std::decay<Ti>::type Args MoveConstructible Destructible, .

f Callable ( , , , - ),
args , _1, _2, _3... std::placeholders

g T std::is_bind_expression<T>::value true. :

std::bind

-

std::bind - std::decay<F>::type, std::forward<F>(f) args... std::decay<Arg_i>::type, std::forward<Arg_i>(arg_i).

std::bind CopyConstructible, - ( ) CopyConstructible, MoveConstructible . :

result_type

1) ( C++17) F -, result_type F. F typedef result_type, result_type F::result_type. result_type .
2) ( C++17) result_type R.
 ( C++20)

operator()

g g(u1, u2, ... uM), ,

1) INVOKE(fd, std::forward<V1>(v1), std::forward<V2>(v2), ..., std::forward<VN>(vN)),
2) INVOKE<R>(fd, std::forward<V1>(v1), std::forward<V2>(v2), ..., std::forward<VN>(vN)),

fd std::decay<F>::type, v1, v2, ..., vN , .

, g(), , g, .

operator() ( C++20) INVOKE. operator() , INVOKE .

g volatile-, .

INVOKE(fd, w1, w2, ..., wN) w1, w2, ..., wN, .

INVOKE INVOKE<R> arg_i v_i :

1:

arg_i std::reference_wrapper<T> (, std::ref std::cref std::bind), v_i arg_i.get() V_i T&: .

2:

arg_i T, std::is_bind_expression<T>::value true (, std::bind std::bind), std::bind : , , , . - -, ( u1, u2, ...). , v_i arg_i(std::forward<Uj>(uj)...), V_i std::result_of<T cv &(Uj&&...)>::type&& ( C++17)std::invoke_result_t<T cv &, Uj&&...>&& ( C++17) (cv- , g).

3:

arg_i T, std::is_placeholder<T>::value 0 ( , , std::placeholders::_1, _2, _3, ..., std::bind), , (u1 _1, u2 _2 ..), : v_i std::forward<Uj>(uj), V_i Uj&&.

4:

arg_i lvalue: v_i arg_i, V_i T cv &, cv cv-, g.

, std::decay<F>::type std::forward<F>(f) , std::decay<Arg_i>::type std::forward<Arg_i>(arg_i) , Arg_i i- , arg_i i- Args... args.

Callable, - (, , , std::shared_ptr std::unique_ptr) , .

, std::ref std::cref.

(, _1) , , (u1) lvalue rvalue. 

#include <functional>
#include <iostream>
#include <memory>
#include <random>

void f(int n1, int n2, int n3, const int& n4, int n5)
{
    std::cout << n1 << ' ' << n2 << ' ' << n3 << ' ' << n4 << ' ' << n5 << '\n';
}

int g(int n1)
{
    return n1;
}

struct Foo {
    void print_sum(int n1, int n2)
    {
        std::cout << n1+n2 << '\n';
    }
    int data = 10;
};

int main()
{
    using namespace std::placeholders;  // for _1, _2, _3...

    std::cout << "1)      : ";
    int n = 7;
    // (_1  _2   std::placeholders,  
    //  ,     f1)
    auto f1 = std::bind(f, _2, 42, _1, std::cref(n), n);
    n = 10;
    f1(1, 2, 1001); // 1   _1, 2   _2, 1001  
                    //  f(2, 42, 1, n, 7)

    std::cout << "2)       : ";
    n = 7;
    auto lambda = [&ncref=n, n](auto a, auto b, auto /* */) {
        f(b, 42, a, ncref, n);
    };
    n = 10;
    lambda(1, 2, 1001); //  ,    f1(1, 2, 1001)

    std::cout << "3)      : ";
    auto f2 = std::bind(f, _3, std::bind(g, _3), _3, 4, 5);
    f2(10, 11, 12); //  f(12, g(12), 12, 4, 5);

    std::cout << "4)  RNG  : ";
    std::default_random_engine e;
    std::uniform_int_distribution<> d(0, 10);
    auto rnd = std::bind(d, e); //  e   rnd
    for(int n=0; n<10; ++n)
        std::cout << rnd() << ' ';
    std::cout << '\n';

    std::cout << "5)     -: ";
    Foo foo;
    auto f3 = std::bind(&Foo::print_sum, &foo, 95, _1);
    f3(5);

    std::cout << "6)   mem_fn,     -: ";
    auto ptr_to_print_sum = std::mem_fn(&Foo::print_sum);
    auto f4 = std::bind(ptr_to_print_sum, &foo, 95, _1);
    f4(5);

    std::cout << "7)      : ";
    auto f5 = std::bind(&Foo::data, _1);
    std::cout << f5(foo) << '\n';

    std::cout << "8)   mem_fn,      : ";
    auto ptr_to_data = std::mem_fn(&Foo::data);
    auto f6 = std::bind(ptr_to_data, _1);
    std::cout << f6(foo) << '\n';

    std::cout << "9)         "
                 " : ";
    std::cout << f6(std::make_shared<Foo>(foo)) << ' '
              << f6(std::make_unique<Foo>(foo)) << '\n';
}

: 

1)      : 2 42 1 10 7
2)       : 2 42 1 10 7
3)      : 12 12 12 4 5
4)  RNG  : 0 1 8 5 5 2 0 7 7 10 
5)     -: 100
6)   mem_fn,     -: 100
7)      : 10
8)   mem_fn,      : 10
9)          : 10 10

C++:

LWG 2021 C++11 1.
     fd
2. 2, V_i
    std::result_of<T cv (Uj...)>::type 		1.
2.
    std::result_of<T cv &(Uj&&...)>::type&&

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