[英]How to write a template wrapper method for other class member functions?
I try to create a templated wrapper for different functions with different parameters. 我尝试使用不同的参数为不同的函数创建模板化包装器。 The setup is a class
A
with the basic implementation of two methods foo
and bar
. 设置是
A
类,基本实现了两个方法foo
和bar
。 Another class B
shall wrap these methods and add new functionality. 另一个
B
类应包装这些方法并添加新功能。
The solution from the following link works very well for non-class functions: c++11: Templated wrapper function 以下链接的解决方案非常适用于非类函数: c ++ 11:模板化包装函数
But if I try to invoke methods from another class I get an error. 但是如果我尝试从另一个类调用方法,我会收到错误。
#include <algorithm>
#include <functional>
#include <iostream>
class A
{
public:
void foo(int x) {
std::cout << "Foo: " << x << std::endl;
}
void bar(int x, float y) {
std::cout << "Bar: " << x << ", " << y << std::endl;
}
};
class B
{
public:
void fooAndMore(int x) {
foobarWrapper(&A::foo, 1);
}
void barAndMore(int x, float y) {
foobarWrapper(&A::bar, 1, 3.5f);
}
template<typename T, typename... Args>
void foobarWrapper(T&& func, Args&&... args)
{
std::cout << "Start!" << std::endl;
std::forward<T>(func)(std::forward<Args>(args)...);
std::cout << "End!" << std::endl;
}
};
int main()
{
B b;
b.fooAndMore(1);
b.barAndMore(2, 3.5f);
}
I expect something like that: 我期待这样的事情:
Start!
Foo: 1
End!
Start!
Bar: 1, 3.5
End!
But instead I get: 但相反,我得到:
error C2064: term does not evaluate to a function taking 1 arguments
note: see reference to function template instantiation 'void B::foobarWrapper<void(__thiscall A::* )(int),int>(T &&,int &&)' being compiled
with
[
T=void (__thiscall A::* )(int)
]
error C2064: term does not evaluate to a function taking 2 arguments
note: see reference to function template instantiation 'void B::foobarWrapper<void(__thiscall A::* )(int,float),int,float>(T &&,int &&,float &&)' being compiled
with
[
T=void (__thiscall A::* )(int,float)
]
Any idea how to solve this? 不知道怎么解决这个问题?
The simplest fix is to make the member functions of class A
to be static
. 最简单的解决方法是使
A
类的成员函数是static
。 ( See online ) ( 见在线 )
class A
{
public:
static void foo(int x) {
^^^^^^
std::cout << "Foo: " << x << std::endl;
}
static void bar(int x, float y) {
^^^^^^
std::cout << "Bar: " << x << ", " << y << std::endl;
}
};
Otherwise, you need to pass an instance of class A
to call its member functions in the foobarWrapper
function. 否则,您需要传递
A
类的实例以在foobarWrapper
函数中调用其成员函数。 Using lambdas you can pack them to the callable func
and pass to the foobarWrapper
. 使用lambdas,您可以将它们打包到可调用的
func
并传递给foobarWrapper
。
( See online ) ( 见在线 )
class B
{
public:
void fooAndMore(const A& a_obj, int x) {
foobarWrapper([&]() { return a_obj.foo(x); });
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^Args captured to the lambda
}
void barAndMore(const A& a_obj, int x, float y) {
foobarWrapper([&]() { return a_obj.bar(x, y); });
// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Args captured to the lambda
}
template<typename T>
void foobarWrapper(T&& func) // no Args needed any more (@credits Jarod42)
{
std::cout << "Start!" << std::endl;
std::forward<T>(func)(); // simply call the func
std::cout << "End!" << std::endl;
}
};
int main()
{
B b;
b.fooAndMore(A{}, 1); // pass a temporary A object
b.barAndMore(A{}, 2, 3.5f);
}
Try this, 试试这个,
#include <algorithm>
#include <functional>
#include <iostream>
class A
{
public:
void foo(int x) {
std::cout << "Foo: " << x << std::endl;
}
void bar(int x, float y) {
std::cout << "Bar: " << x << ", " << y << std::endl;
}
};
class B
{
public:
void fooAndMore(int x) {
foobarWrapper(&A::foo, x);
}
void barAndMore(int x, float y) {
foobarWrapper(&A::bar, x, y);
}
template<typename T, typename... Args>
void foobarWrapper(T func, Args&&... args)
{
std::cout << "Start!" << std::endl;
auto caller = std::mem_fn( func); // Newly added lines
caller( A(), args...); // Newly added line
std::cout << "End!" << std::endl;
}
};
int main()
{
B b;
b.fooAndMore(1);
b.barAndMore(2, 3.5f);
}
output: 输出:
Start!
Foo: 1
End!
Start!
Bar: 2, 3.5
End!
See this link for more details std::mem_fn 有关详细信息,请参阅此链接std :: mem_fn
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.