问题描述
假设我有一个函数 functionProxy，它接受一个泛型参数 function 并调用它的 operator():
Suppose I've got a function functionProxy that takes a generic parameter function and call its operator():
template< typename Function > void functionProxy( Function function ) {
function();
}
<小时>
传递给它的对象可能是:
The object passed to it may be:
一个函子:
a functor:
struct Functor {
void operator()() const {
std::cout << "functor!" << std::endl;
}
};
一个函数:
a function:
void function( ) {
std::cout << "function!" << std::endl;
}
一个 (C++0x) lambda 函数:
a (C++0x) lambda function:
[](){ std::cout << "lambda!" << std::endl; }
int main( )
{
functionProxy( Functor() );
functionProxy( function );
functionProxy( [](){ std::cout << "lambda!" << std::endl; } );
return 0;
}
<小时>
在上述所有情况下，编译器是否能够将 function 内联到 functionProxy 中?
推荐答案
没问题.
它知道function的值和它传递给它的值是一样的，知道函数的定义，所以直接内联替换定义，直接调用函数.
It knows the value of function is the same as the value it passes it, knows the definition of the function, so just replaces the definition inline and calls the function directly.
我想不出编译器不会内联单行函数调用的情况，它只是用函数调用替换函数调用，没有可能的损失.
I can't think of a condition where a compiler won't inline a one-line function call, it's just replacing a function call with a function call, no possible loss.
鉴于此代码:
#include <iostream>
template <typename Function>
void functionProxy(Function function)
{
function();
}
struct Functor
{
void operator()() const
{
std::cout << "functor!" << std::endl;
}
};
void function()
{
std::cout << "function!" << std::endl;
}
//#define MANUALLY_INLINE
#ifdef MANUALLY_INLINE
void test()
{
Functor()();
function();
[](){ std::cout << "lambda!" << std::endl; }();
}
#else
void test()
{
functionProxy(Functor());
functionProxy(function);
functionProxy([](){ std::cout << "lambda!" << std::endl; });
}
#endif
int main()
{
test();
}
定义 MANUALLY_INLINE 后，我们得到:
With MANUALLY_INLINE defined, we get this:
test:
00401000 mov eax,dword ptr [__imp_std::endl (402044h)]
00401005 mov ecx,dword ptr [__imp_std::cout (402058h)]
0040100B push eax
0040100C push offset string "functor!" (402114h)
00401011 push ecx
00401012 call std::operator<<<std::char_traits<char> > (401110h)
00401017 add esp,8
0040101A mov ecx,eax
0040101C call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401022 mov edx,dword ptr [__imp_std::endl (402044h)]
00401028 mov eax,dword ptr [__imp_std::cout (402058h)]
0040102D push edx
0040102E push offset string "function!" (402120h)
00401033 push eax
00401034 call std::operator<<<std::char_traits<char> > (401110h)
00401039 add esp,8
0040103C mov ecx,eax
0040103E call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401044 mov ecx,dword ptr [__imp_std::endl (402044h)]
0040104A mov edx,dword ptr [__imp_std::cout (402058h)]
00401050 push ecx
00401051 push offset string "lambda!" (40212Ch)
00401056 push edx
00401057 call std::operator<<<std::char_traits<char> > (401110h)
0040105C add esp,8
0040105F mov ecx,eax
00401061 call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401067 ret
没有，这个:
test:
00401000 mov eax,dword ptr [__imp_std::endl (402044h)]
00401005 mov ecx,dword ptr [__imp_std::cout (402058h)]
0040100B push eax
0040100C push offset string "functor!" (402114h)
00401011 push ecx
00401012 call std::operator<<<std::char_traits<char> > (401110h)
00401017 add esp,8
0040101A mov ecx,eax
0040101C call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401022 mov edx,dword ptr [__imp_std::endl (402044h)]
00401028 mov eax,dword ptr [__imp_std::cout (402058h)]
0040102D push edx
0040102E push offset string "function!" (402120h)
00401033 push eax
00401034 call std::operator<<<std::char_traits<char> > (401110h)
00401039 add esp,8
0040103C mov ecx,eax
0040103E call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401044 mov ecx,dword ptr [__imp_std::endl (402044h)]
0040104A mov edx,dword ptr [__imp_std::cout (402058h)]
00401050 push ecx
00401051 push offset string "lambda!" (40212Ch)
00401056 push edx
00401057 call std::operator<<<std::char_traits<char> > (401110h)
0040105C add esp,8
0040105F mov ecx,eax
00401061 call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (40204Ch)]
00401067 ret
一样.(与 MSVC 2010 一起编译，原版.)
The same. (Compiled with MSVC 2010, vanilla Release.)
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