c++ - Template template partial specialization - Stack Overflow

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Consider the following class template.

template<template<typename U> typename T>
class Entity {
  // Something
};

What is the proper syntax to specialize Entity explicitly:

• by U,
• by T (keeping it as a template)?

I cannot find out the proper syntax for this task. The cppreference page does not provide any examples on this issue.

Consider the following class template.

template<template<typename U> typename T>
class Entity {
  // Something
};

What is the proper syntax to specialize Entity explicitly:

• by U,
• by T (keeping it as a template)?

I cannot find out the proper syntax for this task. The cppreference page does not provide any examples on this issue.

• c++
• templates
• template-specialization
• partial-specialization
• explicit-specialization

Share Improve this question Follow edited 2 days ago Kaiyakha asked 2 days ago KaiyakhaKaiyakha 1,81311 gold badge1111 silver badges2828 bronze badges 8

• 1 "by U" there are not really U there. – Jarod42 Commented 2 days ago
• There is no syntax to specialize by U, since a "fixed U" changes the argument from a template into a type. The parmeter is T only, and an argument for it would be something like std::vector (no args), whereas std::vector<int> won't be a proper argument since it's a type, not a template. – StoryTeller - Unslander Monica Commented 2 days ago
• "keeping it as a template" Not sure what you mean here. – Jarod42 Commented 2 days ago
• @Jarod42 it means the T parameter must be a concrete template, not just some T template. – Kaiyakha Commented 2 days ago
• @Jarod42 what do you mean by there are not really U there? – Kaiyakha Commented 2 days ago

 |  Show 3 more comments

1 Answer 1

Sorted by: Reset to default 2

Here an example of specialization:

template <template<typename> typename C>
class Entity {
  // Something
};

template <typename>
struct A{};

template <>
class Entity<A>
{
// ...
};
// Usage is Entity<A> entity;

Demo

But you probably want something like:

template <typename T>
class Entity {
  // Something
};

template <typename>
struct A{};

template <typename T>
class Entity<A<T>>
{
    // ...
};

template <typename T, template <typename> class C>
class Entity<C<T>>
{
    // ...
};

// Usage is Entity<A<int>> entity;

Demo

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