Can I specify that template arguments ought to be subclasses of some base class?

Question

I have a class that is designed to work with a certain type of parameter. Is there any way that I can enforce that the template parameter be a pointer to a subclass of some type?

http://stackoverflow.com/questions/3175219/restrict-c-template-parameter-to-subclass — Jason LeBrun, Apr 14 '11 at 02:29
possible duplicate of [C++: Templates of child classes only](http://stackoverflow.com/questions/5612521/c-templates-of-child-classes-only) — Xeo, Apr 14 '11 at 02:30

score 8 · Accepted Answer · answered Apr 14 '11 at 02:31

8

#include <type_traits>
#include <utility>

struct B { };
struct D : B { };

template <typename T>
struct S {
    typedef typename std::enable_if<std::is_base_of<B, T>::value>::type check;
};

int main()
{
    S<B> x;   // Ok!
    S<D> y;   // Ok!
    S<int> z; // Not ok!
}

The enable_if utility and the is_base_of type trait are part of the C++0x Standard Library, but both available in Boost as well.

answered Apr 14 '11 at 02:31

James McNellis

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Could also put that into the template parameters: `template ::value>::type>`. – Xeo Apr 14 '11 at 02:35
Yes, you could, but then your template parameter list quickly gets unwieldy. – James McNellis Apr 14 '11 at 02:38
Personally I find `static B* check = (T*) 0` clear enough. No need to include Boost for just this. – MSalters Apr 14 '11 at 09:04

Can I specify that template arguments ought to be subclasses of some base class?

1 Answers1