CODEWITHSUNDEEP
c++templates
chrise
chrise

Reputation: 4253

C++ converting templates with operator overload

I have a template class where I try to convert a template verision to another via operator overload

enum MyTypes {A,B,C}

template<MyTypes T>
MyClass {
    const static MyType type_ = T;
    template<MyTypes U>       
    MyClass<U> convert(MyTypes t) {
        MyType<U> ret = MyType<U>();
        ....
        return r;
    }
    template<MyTypes U>      
    MyClass<U> operator()() {
        return convert(U);
    }
}

However, this yields (on gcc, c11)

conversion from MyClass<0u> to non-scalar type MyClass<1u> requested

removing the template functions and trying

MyClass<A> operator()() {
    MyClass<A> a = MyClass<A>();
    ...
    return a;
}

throws 

the error operator cannot be overloaded

Basically, what I am trying to achieve is that if I have

MyClass<A> a = MyClass<A>;
MyClass<B> b = a;

that it creates a new MyClass based on a and the conversion. Any idea what my mistake here is?

EDIT: I tossed out one template function, just leaving the operator

template<MyTypes U>      
MyClass<U> operator()() {
    MyClass<U> ret = MyClass<U>();
    ...
    return ret;
}

but this still yields

conversion from MyClass<0u> to non-scalar type MyClass<1u> requested

when trying to do 

MyClass<B> = a

Upvotes: 0

Views: 178

Answers (1)

wally
wally

Reputation: 11002

The following converts the value and allows for the assignment:

#include <iostream>
#include <string>

enum MyTypes { A, B, C };

template<MyTypes T>
struct MyClass{
    const static MyTypes type_ = T;
    std::string history{"started as " + std::to_string(T)};

    template<MyTypes U>
    operator MyClass<U> () {
        return {history+" then became " + std::to_string(U)};
    }
};

int main()
{
    MyClass<A> a;
    MyClass<B> b = a;
    MyClass<C> c = b;

    std::cout << a.history << '\n';
    std::cout << b.history << '\n';
    std::cout << c.history << '\n';
}

Output:

started as 0
started as 0 then became 1
started as 0 then became 1 then became 2

Upvotes: 2

Related Questions