CODEWITHSUNDEEP
c++ooptemplates
AK_is_curious
AK_is_curious

Reputation: 239

Specify template argument by subclassing

When I inherit from a templated class and provide the argument during the inheritence, how do I have to handle functions from the parent class, which use the template argument?

For example with this class as the parent:

template<typename T>
class Parent {
public:
    virtual T someFunction(const T& data);
};

and I try to inherit like this:

class CharVersion : Parent<char> {
public:
    T someFunction(const T& t) override {
        return 'c'
    }
};

How can I get the function in the child to act like:

char someFunction(const char& t) override {
    return 'c'
}

The compiler obviously doesn't know T in the subclass, so how can I express this?

Upvotes: 0

Views: 49

Answers (2)

Doga Oruc
Doga Oruc

Reputation: 816

class CharVersion : Parent<char> {
public:
    T someFunction(const T& t) override {
        return 'c'
    }
};

should be

class CharVersion : Parent<char> {
public:
    char someFunction(const char& t) override {
        return 'c'
    }
};

Upvotes: 1

David Z
David Z

Reputation: 131550

When you write Parent<char>, the compiler effectively generates a class definition as if you had substituted char into the template text. That is, behind the scenes it's as if the parent class of CharVersion is the following template instantiation:

class Parent_char {
public:
    virtual char someFunction(const char& data);
};

You can write your subclass just as if you were extending that class. (Of course, the name of the generated template instantiation is not Parent_char, but that's unlikely to matter.)

Upvotes: 1

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