[boost] template_assert

From: Johan Paulsson (boost.list_at_[hidden])
Date: 2005-03-15 07:09:20

(If this is off topic, has already been discussed, or is stupid, I'm sorry)

I wanted a static assert without #define, I ended up with this:

template<bool MustBeTrue, int TemplateAssertError = 1 / 
static_cast<int>(MustBeTrue)>
  class template_assert {};

so
template_assert<true> means TemplateAssertError = 1 / 1, no error
template_assert<false> means TemplateAssertError = 1 / 0, error

The only compiler I have is MSVC++ 2003. I have no idea how other 
compilers like it, but to me this seems like a better  alternative to 
BOOST_STATIC_ASSERT. Is it?

An example, with the code that will trigger template_assert commented out:

//

template<class Type>
  struct test {
    typedef template_assert<sizeof(Type) == sizeof(int)> assert_type;
    void do_nothing() {}
    };

template<bool Boo>
  void function() {
    template_assert<Boo>();
    test<int> works;
    works.do_nothing();
    //test<char> fails;
    //fails.do_nothing();
    }

void start() {
    function<true>(); //works
    //function<false>(); //fails
    }

//

In MSVC++ 2003 i can also use:

template<bool Boo>
  void function() {
    template_assert<Boo>; //<-- no parenthesis
    ...

but i suppose this is not portable (I don't have a copy of the C++ 
standard).

Thank you all for making boost!

/Johan Paulsson