c + +提升业绩绑定 [英] C ++ Boost Bind Performance

问题描述

（使用Boost绑定）绑定功能时是否有任何性能的影响（正面或负面的）？

Are there any performance impacts (positive or negative) when binding functions (using Boost Bind) ?

推荐答案

也许，也许不是。这要看情况。

Maybe, may not be. It depends.

的std ::绑定的结果（或者也的boost ::绑定）是所谓的结合前pression，里面有一个未与害羞;知道＆害羞;由实现确定能够类型。该类型是的可赎回的，它是的转换的一个在与害羞; 的std ::功能的立场（或的boost ::功能）。

The result of std::bind (or also boost::bind) is a so-called "bind expression", which has an un­know­able type determined by the implementation. This type is a Callable, and it is convertible to an in­stance of std::function (or boost::function).

在内部，函数（5月）使用类型擦除处理各种复杂，有状态的呼叫＆害羞，能够对象。这需要动态分配，并在某些虚拟讯（虽然不是neces＆害羞;纱丽和害羞; LY全部）的情况。无论绑定和函数是有状态的，因为它们存储绑定参数。

Internally, function (may) use type erasure to handle various complex, stateful "call­able objects". This entails a dynamic allocation and a virtual dispatch in some (though not neces­sari­ly all) cases. Both bind and function are stateful, since they store the bound arguments.

其结果是，你应该避免绑定前pression转换为函数对象，如果可能的话。绑定前pression本身可能会更便宜，你不应该害怕使用绑定（例如，当绑定与害羞; ING成员函数指针的实例和参数）。使用绑定自由，但转化为函数只有当你真正需要管理的可调用实体的异类集合。

The upshot is that you should avoid converting a bind expression to a function object if possible. The bind expression itself may be cheaper, and you should not be afraid of using bind (for example when bind­ing member function pointers to instances and arguments). Use bind freely, but conversion to function only if you truly need to manage a heterogeneous collection of callable entities.

下面是两个典型的例子：

Here are two typical examples:

坏;避免这种情况：

std::function<int(bool, char)> f = std::bind(&Foo::bar, x, 12);

void do_something(std::function<int()> func, int & acc)
{
    acc += func();
}

更好; preFER这样的：

auto f = std::bind(&Foo::bar, x, 12);   // unknowable type, but perfectly fine

template <typename F>
void do_something(F && func, int & acc)  // can deduce unknowable types
{
    acc += func();
}

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