CODEWITHSUNDEEP
c++templatespartial-specialization
Zebrafish
Zebrafish

Reputation: 14390

How to check if a template argument is of a particular templated type (multiple type parameters)

I asked a question yesterday (How to find out if a type is a templated type of any type?) about how to check for a particular template argument when that argument is a templated class of any type. And the solution was something like this:

template <typename T>
struct Animal{};

template <typename T>
struct IsAnimalOfAnyType
{
    constexpr bool value() { return false; }
};

template <typename T>
struct IsAnimalOfAnyType<Animal<T>>
{
    constexpr bool value() { return true; }
};

However this works with single-argument templates, but I'm trying to do the following:

template <typename T, T integer, typename U>
struct Animal{};

template <typename T>
struct IsAnimalOfAnyType
{
    constexpr bool value() { return false; }
};


template <typename T> 
struct IsAnimalOfAnyType<Animal<T>>
{
    constexpr bool value() { return true; }
};

/* Animal needs to be Animal<T, integer, U>,
  but 'T', 'integer' and 'U' template arguments are not available here,
  and if I have these arguments here
  then IsAnimalOfAnyType is no longer a specialization and it won't compile
*/

As far as I understand it the difference is that struct Animal:

  1. Has multiple template arguments and
  2. One of the arguments is not a type, but an integer

How to go about doing this?

Upvotes: 4

Views: 84

Answers (1)

songyuanyao
songyuanyao

Reputation: 173034

You can declare all the template parameters required by Animal for the specialization.

template <typename T, T integer, typename U> 
struct IsAnimalOfAnyType<Animal<T, integer, U>>
{
    constexpr bool value() { return true; }
};

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Upvotes: 4

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