@STL: std:function still have overhead which makes it less usable for doing small things. Like using in a scope guard class or special callbacks, etc..
Take this code and compile it in release mode / win32 and look at it in debugging.
#include <iostream>
#include <functional>
using namespace std;
inline void func() {
cout << "func" << endl;
}
struct s_func {
inline void operator()() {
cout << "s_func" << endl;
}
};
template <typename Functor>
void test_template(Functor f) {
f();
}
void test_function(function<void()> f) {
f();
}
int main()
{
test_template(func);
test_function(func);
test_template(s_func());
test_function(s_func());
}
test_template(func):
test_template(func); 00301095 mov eax,dword ptr [__imp_std::endl (302044h)] 0030109A mov ecx,dword ptr [__imp_std::cout (302068h)] 003010A0 push eax 003010A1 push offset string "func" (30214Ch) 003010A6 push ecx 003010A7 call std::operator<<<std::char_traits<char> > (301240h) 003010AC add esp,8 003010AF mov ecx,eax 003010B1 call dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (30204Ch)]
test_function(func); : (called functions not included)
test_function(func); 003010B7 mov edx,offset func (301040h) 003010BC test edx,edx 003010BE jne main+54h (3010C4h) 003010C0 xor ecx,ecx 003010C2 jmp main+65h (3010D5h) 003010C4 mov dword ptr [ebp-24h],offset std::tr1::_Impl_no_alloc0<std::tr1::_Callable_fun<void (__cdecl*const)(void),0>,void>::`vftable' (302188h) 003010CB mov dword ptr [ebp-20h],offset func (301040h) 003010D2 lea ecx,[ebp-24h] 003010D5 mov dword ptr [ebp-14h],ecx 003010D8 mov dword ptr [ebp-4],0 003010DF test ecx,ecx 003010E1 jne $LN163 (3010E9h) 003010E3 call dword ptr [__imp_std::tr1::_Xfunc (302064h)] $LN163: 003010E9 mov eax,dword ptr [ecx] 003010EB mov edx,dword ptr [eax+4] 003010EE call edx 003010F0 mov dword ptr [ebp-4],0FFFFFFFFh 003010F7 mov ecx,dword ptr [ebp-14h] 003010FA test ecx,ecx 003010FC je $LN163+28h (301111h) 003010FE mov eax,dword ptr [ecx] 00301100 mov eax,dword ptr [eax+0Ch] 00301103 lea edx,[ebp-24h] 00301106 cmp ecx,edx 00301108 setne dl 0030110B movzx edx,dl 0030110E push edx 0030110F call eax
function 'test_template' is a clear winner. Now the sad part is that you can't do this in a class without overhead because you have to store the function object which isn't really supported so you have to resort to tricks which have overhead.
// class version equivalent to test_template
// This should have been supported but nope
class scope_guard {
auto f;
public:
template <typename Functor>
scope_guard(Functor f_obj) : f(f_obj) { // <- ???
}
~scope_guard() {
f();
}
function "test_template" works because you don't have to store the function object
