boost绑定类函数指针 [英] boost bind class function pointer

问题描述

class Foo 
{
    double f1( int x, std::string s1 );
    double f2( int x, SomeClass s2 );
}

我想要能绑定Foo.f1的s1没有foo的实例

I want to be able to bind Foo.f1's s1 without an instance of foo to create in essense

typedef double (Foo::* MyFooFunc)( int ) 

MyFooFunc func1 = boost::bind( &Foo::f1, _1, _2, "some string" );
MyFooFunc func2 = boost::bind( &Foo::f2, _1, _2, SomeClass );

然后我将func1和func2作为参数传递给其他函数，其中Foo终于绑定：

Then I pass func1 and func2 as parameters to other functions, inside which Foo is finally bound:

void SomeOtherFunction( MyFooFunc func )
{
     Foo foo;
     boost::function< double (int) > finalFunc =
          boost::bind( func, foo, _1 );
}

问题：
这是可能吗？如果是，1）如何实现呢？ 2）什么是MyFooFunc的声明？

Questions: Is this possible? If yes, 1) how to achieve it? 2) What's the declaration of MyFooFunc?

推荐答案

typedef double (Foo::* MyFooFunc)( int );

MyFooFunc func1 = boost::bind( &Foo::f1, _1, _2, "some string" );

boost :: bind 的结果是不是指向成员的指针，因此 func1 不能像第二行那样初始化。 boost :: bind 的结果是未指定的类型（这将取决于参数）。如果你使用C ++ 0x，调用 bind 的最简单的方法是使用 auto ：

The result of boost::bind is not a pointer to member, so func1 cannot be initialized as such on the second line. The result of boost::bind is an unspecified type (which will depend on the parameters). If you're using C++0x, the simplest way to name the result of a call to bind is to use auto:

auto func1 = boost::bind( &Foo::f1, _1, _2, "some string" );

另一种简单的方法（不限于C ++ 03）现在使用它：

Another simple way (not restricted to C++03) is simply to not name the result, but to use it on the spot:

SomeOtherFunction(boost::bind(&Foo::f1, _1, _2, "some string"));

或者，可以使用type-erasure存储 boost的结果： ：bind 添加到您似乎熟悉的 boost :: function 中。 boost :: function< double（Foo& int）> 是一种可能性，但不是唯一的选择。

Or, you can use type-erasure to store the result of boost::bind into a boost::function, which you seem to be familiar with. boost::function<double(Foo&, int)> is a possibility but not the only choice.

我们现在需要为 SomeOtherFunction 找到适当的签名：再次，指向成员的指针不能从结果初始化调用 boost :: bind ，所以 void SomeOtherFunction（MyFooFunc func）; 将无法工作。您可以使该函数成为模板：

We now need to find the appropriate signature for SomeOtherFunction: again, a pointer to member can't be initialized from the result of a call to boost::bind, so void SomeOtherFunction(MyFooFunc func); won't work. You can make the function a template instead:

template<typename Func>
void SomeOtherFunction( Func func )
{
     Foo foo;
     boost::function< double (int) > finalFunc =
          boost::bind( func, foo, _1 );
}

如果模板不是首选，那么必须使用某种类型 - 擦除，例如， boost :: function 。

If a template is not preferrable, then you must use some kind of type-erasure such as, again, boost::function.

void SomeOtherFunction(boost::function<double(Foo&, int)> const& func);

（另一次 boost :: function 类型是可能的，取决于细节，例如传递一个ref-to-const而不是一个ref-to-non-const）

(once again other boost::function types are possible depending on details such as passing a ref-to-const as opposed to a ref-to-non-const)

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