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std::bind

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Os operadores relacionais
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Relational operators
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rel_ops::operator!=
rel_ops::operator>
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Pares e tuplas
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Pairs and tuples
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Swap, forward and move
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Objetos de função


Invólucros de função
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Function wrappers
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(C++11)
(C++11)
(C++11)
Ligar
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Bind
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bind
(C++11)
(C++11)
(C++11)
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Invólucros de referência
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Reference wrappers
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Invólucros operador
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Operator wrappers
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Negadores
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Negators
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Obsoleta ligantes e adaptadores
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Deprecated binders and adaptors
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(obsoleta)
(obsoleta)
(obsoleta)
(obsoleta)
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(obsoleta)
(obsoleta)(obsoleta)(obsoleta)(obsoleta)
(obsoleta)
(obsoleta)(obsoleta)(obsoleta)(obsoleta)
(obsoleta)(obsoleta)
(obsoleta)(obsoleta)
 
Definido no cabeçalho <functional>
template< class F, class... Args >
/*unspecified*/ bind( F&& f, Args&&... args );
 (1) (desde C++11)
template< class R, class F, class... Args >
/*unspecified*/ bind( F&& f, Args&&... args );
 (2) (desde C++11)
O modelo bind função gera um invólucro de encaminhamento de chamadas para f. Chamar esse envoltório é equivalente a chamar f com alguns de seus argumentos vinculados a args.
Original:
The function template bind generates a forwarding call wrapper for f. Calling this wrapper is equivalent to invoking f with some of its arguments bound to args.
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Internamente, o invólucro contém um objeto membro da std::decay<F>::type tipo construído a partir de std::forward<F>(f), e um objeto por cada um dos args..., de std::decay<Arg_i>::type tipo, da mesma forma construído a partir de std::forward<Arg_i>(arg_i).
Original:
Internally, the wrapper holds a member object of type std::decay<F>::type constructed from std::forward<F>(f), and one object per each of args..., of type std::decay<Arg_i>::type, similarly constructed from std::forward<Arg_i>(arg_i).
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Índice

[editar] Parâmetros

f -
invocável objeto (objeto de função, o ponteiro para a função, a referência a função, o ponteiro para função de membro, ou ponteiro para dados de membro), que será obrigado a alguns argumentos
Original:
invocable object (function object, pointer to function, reference to function, pointer to member function, or pointer to member data) that will be bound to some arguments
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args -
lista de argumentos para vincular, com os argumentos não ligados substituído pelo _1, _2, _3... espaços reservados
Original:
list of arguments to bind, with the unbound arguments replaced by the placeholders _1, _2, _3...
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[editar] Valor de retorno

Um objeto da função T tipo não especificado, para o qual std::is_bind_expression<T>::value == true, e que pode ser armazenada em std::function. O objecto é móvel e se f todos args são móveis e, em caso contrário é copiável. O tipo define os seguintes membros:
Original:
A function object of unspecified type T, for which std::is_bind_expression<T>::value == true, and which can be stored in std::function. The object is movable if f and all args are movable, and is copyable otherwise. The type defines the following members:
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std :: bind
Original:
std::bind
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 Return type

Member type result_type

1) If F is a pointer to function or a pointer to member function, result_type is the return type of F. If F is a class type with nested typedef result_type, then result_type is F::result_type. Otherwise no result_type is defined.

2) result_type is exactly R.

Member function operator()

Given an object g obtained from an earlier call to bind, when it is invoked in a function call expression g(u1, u2, ... uM), an invocation of the stored object of type std::decay<F>::type takes place, with arguments defined as follows:

  • If the argument is of type std::reference_wrapper<T> (e.g. std::ref or std::cref) was used in the initial call to bind, then the reference T& stored in the bound argument is passed to the invocable object.
  • If std::is_bind_expression<T>::value == true (i.e. another sbind subexpression was used as an argument in the initial call to bind), then that bind-subexpressin is invoked immediately and its result is passed to the invocable object. If the bind subexpression has any placeholder arguments, they are picked from u1, u2, ....
  • If std::is_placeholder<T>::value != 0 (i.e., _1, _2, _3, ... was used as the argument to the initial call to bind), then the argument indicated by the placeholder (u1 for _1, u2 for _2, etc) is passed to the invocable object as std::forward<Uj>(uj).
  • Otherwise, the stored argument is passed to the invocable object as-is.

If some of the arguments that are supplied in the call to g() are not matched by any placeholders stored in g, the unused arguments are evaluated and discarded.

[editar] Exceções

Só se a construção de lança std::decay<F>::type std::forward<F>(f) de lança, ou qualquer um dos construtores para std::decay<Arg_i>::type do std::forward<Arg_i>(arg_i) corrsponding lança onde Arg_i é o tipo de ordem i e arg_i é o i-ésimo argumento em Args... args.
Original:
Only throws if construction of std::decay<F>::type from std::forward<F>(f) throws, or any of the constructors for std::decay<Arg_i>::type from the corrsponding std::forward<Arg_i>(arg_i) throws where Arg_i is the ith type and arg_i is the ith argument in Args... args.
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[editar] Notas

Os argumentos para se ligam são copiados ou movidos, e nunca são passados ​​por referência a menos envolto em std::ref ou std::cref.
Original:
The arguments to bind are copied or moved, and are never passed by reference unless wrapped in std::ref or std::cref.
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Duplicar espaços reservados na expressão ligam mesmo (múltipla _1, por exemplo) são permitidos, mas os resultados só são bem definido se o argumento correspondente (u1) é um rvalue lvalue ou não-móvel.
Original:
Duplicate placeholders in the same bind expression (multiple _1's for example) are allowed, but the results are only well defined if the corresponding argument (u1) is an lvalue or non-movable rvalue.
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[editar] Exemplo

#include <random>
#include <iostream>
#include <functional>
 
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;
 
    // demonstrates argument reordering and pass-by-reference
    int n = 7;
    auto f1 = std::bind(f, _2, _1, 42, std::cref(n), n);
    n = 10;
    f1(1, 2, 1001); // 1 is bound by _1, 2 is bound by _2, 1001 is unused
 
    // nested bind subexpressions share the placeholders
    auto f2 = std::bind(f, _3, std::bind(g, _3), _3, 4, 5);
    f2(10, 11, 12);
 
    // common use case: binding a RNG with a distribution
    std::default_random_engine e;
    std::uniform_int_distribution<> d(0, 10);
    std::function<int()> rnd = std::bind(d, e);
    for(int n=0; n<10; ++n)
        std::cout << rnd() << ' ';
    std::cout << '\n';
 
    // bind to a member function
    Foo foo;
    auto f3 = std::bind(&Foo::print_sum, foo, 95, _1);
    f3(5);
 
    // bind to member data
    auto f4 = std::bind(&Foo::data, _1);
    std::cout << f4(foo) << '\n';
}

Saída: 

2 1 42 10 7
12 12 12 4 5
1 5 0 2 0 8 2 2 10 8
100
10

[editar] Veja também

(C++11)
espaços reservados para os argumentos não ligados em uma expressão de std::bind
Original:
placeholders for the unbound arguments in a std::bind expression
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(constante) [edit]
(C++11)
cria um objecto de função de um apontador para um membro
Original:
creates a function object out of a pointer to a member
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(modelo de função) [edit]
Obtida de "https://pt.cppreference.com/mwiki/index.php?title=cpp/utility/functional/bind&oldid=26629"