Question

I just encountered a problem with the CRTP, where I can't have the same method name (with a different signature) in both the base and derived class. The example to reproduce this issue is the following :

template <class T>
struct Base
{
    void foo(){}
    void bar(){
        static_cast<T*>(this)->foo(1,1);
    }
};

struct Derived : public Base<Derived>
{
    int foo(int a,int b){ return a+b;}
};

int test()
{
  Derived d;
  d.bar(); // works
  d.foo(1,1); // obviously works
  d.foo(); // compilation error
}

I tried this under various versions of GCC, clang and even ICC using godbolt

Anybody could explain what is at work here ?

GCC output:

In function 'int test()':
22 : error: no matching function for call to 'Derived::foo()'
d.foo(); // doesn't work
^
13 : note: candidate: int Derived::foo(int, int)
int foo(int a,int b){ return a+b;}

Answer 1

It has nothing to do with CRTP, just that the Derived::foo shadows Base::foo, just as if you had declared a foo in an inner scope.

One way to un-shadow the Base version, is to ^[1]place a

using Base<Derived>::foo;

in Derived.

^{^[1] Full example at (http://coliru.stacked-crooked.com/a/5dc7558e12babbe5).}

CRTP with derived class overloading the method

1 个答案: