Question

static_assert seems to be a very nice feature together with templates.

However, I have trouble finding functions in the standard library for doing various tests at compile time.

For example, I am looking for a function to check whether a type is a subtype of another one. boost::is_base_of does the job, however, is a comparable function in std, so I do not need to rely on boost.

Basically, is there a good source for a list of functions which can be used in static_assert and are contained in the standard library of C++11?

When is static_assert executed? Can I put it anywhere in a template and it is evaluated for each template instanciation? Could it be used to constrain template parameters to be a specific subtype of a class?

Answer 1

Take a look at the final C++11 draft, section 20.7, particularly the <type_traits> header.

What you are asking is: std::is_base_of<base, derived>::value;

Regarding your question: static_assert can be evaluated whenever the compiler sees fit, but it will usually:

• In a template: if the expression uses dependent names, in instatiation time; else, in definition time.
• Out of template: in definition time.