C syntactic sugar for two phase look-up-CodePudding

I am trying to provide an API where an user can statically inherit from a base class and use its methods.

The issue is that the class is templated with typename T and the methods are templated with typename U, such that the use of the methods is really cumbersome (I think, for an API).

As far as I understood this is intended since the compiler cannot resolve (the dependent?) methods.

template<typename T>
struct base {
    template<typename U>
    void foo(){}
};

template<typename B>
struct child : B
{
    void barr(){
        B::template foo<float>();
        this->template foo<float>();

        /* 
        B::foo<float>(); - ERROR: expected primary-expression before ‘float’
        this->foo<float>(); - ERROR: expected primary-expression before ‘float’
        foo<float>(); - ERROR:  error: ‘foo’ was not declared in this scope 
        */
    }
};

int main(){

    child<base<bool>> c;
    c.barr();

    return 0;
}

Is there any way that I could get rid of template keyword in the call to foo? Maybe some syntactic sugar I don't know of?

CodePudding user response：

You could add a foo member function template to child that just calls the one in B. That is,

template<typename T>
struct base {
    template<typename U>
    void foo() {}
};

template<typename B>
struct child : B
{
    void barr() {
        foo<float>();
    }

    template<typename T>
    void foo() {
        typename B::template foo<T>();
    }
};

CodePudding user response：

The problem is indeed caused by the compiler's need to resolve foo before deciding that foo< isn't calling operator< on the expression foo. Adding template means that the compiler knows foo< is the start of a template argument list.

As the author of base, there's nothing you can do about that. That's the whole point of the two-phase compilation. The compiler trips over the foo< in the first pass, where all it knows is that child<B> inherits from some unknown B.