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c++templatestemplate-specialization
sajas
sajas

Reputation: 1599

Specializing a template class to take a pointer to a particular class or a pointer to a derived class object

How can I specialize a class template so that the template parameters can be of type : a pointer to a particular class or a pointer to the derived class of that particular type? Is it possible to do it without using Boost?

Possible Duplicate of: C++ templates that accept only certain types

I just wanted to know whether the answer is same even if I am using a pointer to the instances .

Upvotes: 2

Views: 539

Answers (2)

Joseph Mansfield
Joseph Mansfield

Reputation: 110768

You could specialize your class for pointers and then use std::is_base_of with a static_assert:

template <typename T>
class foo;

template <typename T>
class foo<T*>
{
  static_assert(std::is_base_of<Base, T>::value, "Type is not a pointer to type derived from Base");
};

See it in action. Both std::is_base_of and static_assert are C++11 features so no Boost is required.

If for some reason you don't like static_assert, you could do it the enable_if way:

template <typename T, typename Enable = void>
class foo;

template <typename T>
class foo<T*, typename std::enable_if<is_base_of<Base, T>::value>::type>
{
  // ...
};

Upvotes: 5

R. Martinho Fernandes
R. Martinho Fernandes

Reputation: 234654

A technique for having specializations based on some predicate instead of a pattern is to use an extra defaulted parameter.

template <typename T, bool = predicate<T>::value>
class foo {
    // here is the primary template
};

template <typename T>
class foo<T, true>  {
    // here is the specialization for when the predicate is true
};

All you need is a proper predicate. In this case, std::is_base_of seems to fit. There is a boost implementation of it too.

Upvotes: 1

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