[boost] Re: type_traits: has_copy_constructor<>

From: Alexander Nasonov (alnsn-mycop_at_[hidden])
Date: 2003-09-30 10:50:54

David Abrahams wrote:
> All types have a copy_ctor.  It's just a question of whether it's
> private or not, and I'm not sure that's detectable without causing an
> error.

I've just typed something but I'm not sure whether it should work as 
expected. Intel 7.1 compiles it and prints 1 in both cases. Comeau online 
compiles it as well but I can't run the test.
I'll think about this at home with a printed standard in hands.

struct no_copy_ctor {};

template<class T>
struct tester : T
{
    tester();
    tester(const tester& other)
        : T(static_cast<T const&>(other)) {}

    operator no_copy_ctor();
};

typedef char yes_type;
typedef char (&no_type)[2];

template<class T>
yes_type test_copy_ctor(tester<T>);

no_type test_copy_ctor(no_copy_ctor);

template<class T>
struct has_copy_ctor
{
    static const bool value = sizeof(test_copy_ctor(tester<T>())) == 
sizeof(yes_type);
};

// test program
#include <iostream>

class X {};

class Y
{
    Y(const Y&);
};

int main()
{
    std::cout << has_copy_ctor<X>::value << '\n';
    std::cout << has_copy_ctor<Y>::value << '\n';
}

-- 
Alexander Nasonov
Remove minus and all between minus and at from my e-mail for timely response