Thread: Lambda as argument to functor

Foo works as expected. The "Bar" function object does not. For starters, why can I pass a lambda as an argument to Foo, but not to Bar?

Also, how can I achieve the construction of a bar like I'm trying to do in main?

Code:

template <class _Fxn>
void Foo(_Fxn fxn)
{
    fxn();
}

template <class _Fxn>
class Bar
{
    _Fxn fxn;

public:

    Bar(_Fxn f) : fxn(f) {}
    void operator()(){ fxn(); }
};

int main()
{
    Foo([]()->void{ std::cout << "Hello World!\n"; });

    Bar<void()> bar([]()->void{ std::cout << "Hello World!\n"; }); // DOESN'T WORK

}

This is the error I get for trying to construct the bar in main:

Code:

Error	1	error C2664: 'Bar<_Fxn>::Bar(_Fxn (__cdecl *))' : cannot convert parameter 1 from '`anonymous-namespace'::<lambda1>' to 'void (__cdecl *)(void)'	c:\projects\_cs350\helix\helix.cpp	30	1	Helix

Like the error says, you are saying that the type _Fxn for Bar is void(), but the actual type for a lambda isn't that. It's something else.
Perhaps you should try

Code:

auto lambda = []() { std::cout << "Hello World!\n"; };
Bar<decltype(lambda)> bar(lambda);