Doing a static_assert that a template type is another template

Question

How do I static_assert like this? Maybe Boost supports it if not C++ or new features in C++11?

template
struct foo {};

template

        

Answer 1

Some small improvements over the other answers:

• the name actually makes sense regarding the order of the parameters
• handles const, volatile, and reference types properly via std::decay
• implements C++14-style _v constexpr variable
• accepts an arbitrary number of types to test against (tests for ALL)

I have intentionally not put the std::decay_t on the is_template_for_v because a type trait should work identically regardless of whether it is called with the _v suffix or not.

This does require C++17 for std::conjunction, but you can either remove the variadic feature or implement your own conjunction using c++11/14.

template class tmpl, typename T>
struct _is_template_for : public std::false_type {};

template class tmpl, class... Args>
struct _is_template_for> : public std::true_type {};

template class tmpl, typename... Ts>
using is_template_for = std::conjunction<_is_template_for>...>;

template class tmpl, typename... Ts>
constexpr bool is_template_for_v = is_template_for::value;

Usage:

static_assert(is_template_for_v>); // doesn't fire