A single C++ header file for SFINAE-able error messages. Templated code with SFINAE-able error messages is easier to debug, and doesn't suffer from the inflexibility that comes with static_assert.
#include <type_traits>
#include "sfinae_errors.hpp"
// An error "origin" describes the source of the substitution failure
DEFINE_SFINAE_ERROR_ORIGIN(const_copyable)
// T_must_be_const and T_must_be_copy_constructible are
// SFINAE "exceptions", associated with const_copyable
DEFINE_SFINAE_ERROR_FOR(const_copyable, T_must_be_const)
DEFINE_SFINAE_ERROR_FOR(const_copyable, T_must_be_copy_constructible)
// This is an alias template that aliases T, but SFINAEs
// when T is not const or when T is not copy constructible.
// Note that if the aliased type is a template, it is not
// instantiated until after the checks are performed.
template<typename T>
using const_copyable = sfinae_errors::sfinae_try< T,
sfinae_errors::fail_if<!std::is_copy_constructible<T>::value, T_must_be_copy_constructible>,
sfinae_errors::fail_if<!std::is_const<T>::value, T_must_be_const>
>;
int main(){
// compiler error:
// no type named 'type' in 'error::const_copyable<T_must_be_const_>::_'
const_copyable<int> i = 0;
return i;
}
- Clang 3.4 and later
- GCC 4.7.3 and later
- Visual Studio 2015
Older platforms are untested.
Distributed under the Boost software license.