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C ++ partial specialization: how can I highlight this template <class T1, class T2> into this template <class T1>?

#include <iostream>
using namespace std;

template <class T1, class T2>
class A {
public:
    void taunt() { cout << "A"; }
};

template <class T1>
class A<T1, T1> {
public:
    void taunt() { cout << "B"; }
};

class B {};

class C {};

int main (int argc, char * const argv[]) {

    A<B> a;

    return 0;
}

How can I convert my two parameter templates to a single parameter template?

The above code will give a compiler error in 'A a;' for "wrong number of template arguments".

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2 answers

Template specialization cannot be used to reduce the number of template arguments, for this you must use the default values ​​for some arguments.

So, to allow the use of only one argument and make this use successful in your area of ​​expertise, you need a second argument by default, which matches the first argument:

#include <iostream>
using namespace std;

template <class T1, class T2=T1>
class A {
public:
    void taunt() { cout << "A"; }
};

template <class T1>
class A<T1, T1> {
public:
    void taunt() { cout << "B"; }
};

class B {};

class C {};

int main (int argc, char * const argv[]) {

    A<B> a;
    a.taunt(); // Prints "B"

    return 0;
}
+6

() :

template <class T1, typename T2 = void>
class A {
public:
    void taunt() { cout << "A"; }
};
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