mem_fn到成员对象的功能 [英] mem_fn to function of member object
本文介绍了mem_fn到成员对象的功能的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我正在修改std::mem_fn
,无法将其绑定到结构成员(更深一层)的数据/功能.
I was tinkering around with the std::mem_fn
and couldn't manage to bind it to data/functions of an member of a struct (one layer deeper).
我希望代码能比我描述的更好地显示问题,因为我对术语不熟悉.
I hope that the code shows the problem better than I can describe it, because I'm not familiar with the terminology.
#include <functional>
struct Int
{
Int(int _x = 0) : x(_x) {}
int GetInt() const { return x; }
int x;
};
struct IntWrapper
{
IntWrapper(int _x = 0) : test(_x) {}
int GetWrappedInt() const { return test.GetInt(); }
Int test;
};
int main()
{
IntWrapper wrapper{ 123 };
auto x = std::mem_fn(&IntWrapper::GetWrappedInt);
//auto y = std::mem_fn(&IntWrapper::test.GetInt); // ERROR
//auto z = std::mem_fn(&IntWrapper::test.x); // ERROR
int a = x(wrapper);
//int b = y(wrapper);
//int c = z(wrapper);
//std::cin.ignore();
return 0;
}
错误消息如下:
error C2228: left of '.GetInt' must have class/struct/union
error C2672: 'std::mem_fn': no matching overloaded function found
error C3536: 'y': cannot be used before it is initialized
error C2064: term does not evaluate to a function taking 1 arguments
问题:
是否可以进行这些绑定?我需要std::bind
吗?
Question:
Is it possible to make these binds? Do I need std::bind
for this?
推荐答案
According to the specification, std::mem_fn()
takes as argument a member function pointer, i.e.
auto y = std::mem_fn(&Int::GetInt);
auto b = y(wrapper.test);
据我所知,std::mem_fn()
或多或少已经过时,因为 lambda表达式.例如
As far as I'm aware, std::mem_fn()
is more or less obsolete, since lambda expressions. For example
auto y = [](IntWrapper const&wrapper) { return wrapper.test.GetInt(); };
auto b = y(wrapper); // note: no need to get hold of member 'test'
这篇关于mem_fn到成员对象的功能的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文