CODEWITHSUNDEEP
c++templatespartial-specialization
Alex
Alex

Reputation: 1175

Template template partial specialization failure: "expected a class template"

This example code generates expected a class template, got std::pair <_T1, _T2>. I tried using struct Struct <std::pair> {};, but then parameters T and M become undeducible. How to avoid this?

    template <template <class...> class>
    struct Struct {};

    template <class T, class M>
    struct Struct <std::pair <T, M>> {};

Upvotes: 3

Views: 2205

Answers (2)

Jarod42
Jarod42

Reputation: 217075

Depending of what you want

template <template <class...> class>
struct Struct {};

template <>
struct Struct <std::pair>
{
    // Specialization
};

or

template <typename> struct Struct {};

template <typename First, typename Second>
struct Struct <std::pair<First, Second>>
{
    // Specialization
};

Upvotes: 4

Rerito
Rerito

Reputation: 6086

That is not a valid specialization for your template.

The reason why is because std::pair<T, M> is a full specialization of the class template std::pair and therefore a class. Your template expects a class template parameter which is exactly what the compiler is telling you.

Upvotes: 2

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