继承的模板类的构造函数

Question

In the following code, I want to keep inheritance class B : public A<F> , but want to pass globalFunction() only to A and accessed from B as A::f1() and A::fa(). How can I do that?

#include <iostream>

void globalFunction()
{ }

//passing function to class A from main()
template<typename F>
class A
{
public:
    F f1;
    A(F fun1) : f1(fun1) {}
    void fa() {  f1();  } ;
};


template<typename F>
class B : public A<F>
{
public:
    B (F fun2) : A<F>(fun2) {}
    void fb() ; 
};

template<typename F>
void B<F>::fb() { A<F>::f1(); }

int main()
{
    A obja(globalFunction);
    obja.fa();
    B objb(globalFunction);
    objb.fb();
}

Basically I want to avoid making B as B<F> . Does inheriting A<F> to B makes B also a template B<F> ? I am not using template argument F anywhere in B , it is just inherited from A and using from B as A<F>::f1()

User will pass function globalFunction to templated argument so, class B : public A<decltype(globalFunction)> cannot be used.

Answer 1

If you know that your functor type is always going to be a function of a certain signature, you can get rid of templates altogether:

void globalFunction()
{ }

//passing function to class A from main()

class A
{
public:
    using fptr_t = void (*)();
    fptr_t f1;
    A(fptr_t fun1) : f1(fun1) {}
    void fa() {  f1();  } ;
};


class B : public A
{
public:
    B (fptr_t fun2) : A(fun2) {}
    void fb() ; 
};

void B::fb() { A::f1(); }

int main()
{
    A obja(globalFunction);
    obja.fa();
    B objb(globalFunction);
    objb.fb();
}

That is slightly detrimental to performance, since you would not be able to inline calls to your function pointers, but it does get rid of a template as requested.