CODEWITHSUNDEEP
c++templatestemplate-specialization
SmileyCraft
SmileyCraft

Reputation: 257

Multiple conditional template specialization c++

I have a struct

template <typename A, typename B>
struct foo {static const int type = 0;};

I want the implementation to be different when both A and B are arithmetic. However this did not work.

template <typename A, typename B, typename std::enable_if<
        std::is_arithmetic<A>::value && 
        std::is_arithmetic<B>::value, bool>::type = 0>
struct foo<A, B> {static const int type = 1;}

I get the compiler error default template arguments may not be used in partial specializations. So how can I make this work?

One thing to keep in mind is that I also want to have other simpler template specializations that might look like this.

template <>
struct foo<string, vector<int>> {static const int type = 2;}

In summary, I want the first definition to be like a default, and then define a bunch of specialized implementations, one of which is kind of general.

Upvotes: 2

Views: 486

Answers (1)

songyuanyao
songyuanyao

Reputation: 172924

You could define the primary template, partial specialization and full specialization separately like

// the primary template
template <typename A, typename B, typename = void>
struct foo {static const int type = 0;};

// the partial specialization
template <typename A, typename B>
struct foo<A, B, typename std::enable_if<
        std::is_arithmetic<A>::value && 
        std::is_arithmetic<B>::value>::type> {static const int type = 1;};

// the full specialization
template <>
struct foo<string, vector<int>, void> {static const int type = 2;};

LIVE

Upvotes: 4

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