Re: Template-Meta: Finding out whether a template-definition exists
On 9 3 , 8 13 , "Hendrik Schober" <SpamT...@gmx.de> wrote:
Hi,
suppose we have
template< typename T >
struct X;
and some specializations:
template<>
struct X<A> {};
template<>
struct X<B> {};
template<>
struct X<B> {};
Given a type 'U', is there a way to find out whether the
definition 'X<U>' exists? (The result should be a compile-
time constant, so that it can be used for specializing
other templates.)
after revising the code I post else-thread, it seems to work as you
wish
#include <iostream>
using namespace std;
template <class T>
struct X;
template <>
struct X<int>
{
};
template <>
struct X<float>
{
};
template <class U>
struct is_specialized
{
struct true_type
{
char dummy[256];
};
struct false_type
{
char dummy[1];
};
template <class T>
static true_type test(X<T>);
static false_type test(...);
template <class T>
static X<T> make_xt();
enum { value = (sizeof(test(make_xt<U>())) ==
sizeof(true_type)) };
};
int main()
{
cout << is_specialized<int>::value << endl;
cout << is_specialized<float>::value << endl;
cout << is_specialized<bool>::value << endl;
}
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