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// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
#include <boost/hana/core/default.hpp>
#include <boost/hana/core/tag_of.hpp>
#include <boost/hana/integral_constant.hpp>
#include <string>
#include <type_traits>
namespace hana = boost::hana;
namespace with_special_base_class {
//! [special_base_class]
struct special_base_class { };
template <typename T>
struct print_impl : special_base_class {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
template <typename T>
struct Printable
: hana::integral_constant<bool,
!std::is_base_of<special_base_class, print_impl<hana::tag_of_t<T>>>::value
>
{ };
//! [special_base_class]
//! [special_base_class_customize]
struct Person { std::string name; };
template <>
struct print_impl<Person> /* don't inherit from special_base_class */ {
// ... implementation ...
};
static_assert(Printable<Person>::value, "");
static_assert(!Printable<void>::value, "");
//! [special_base_class_customize]
}
namespace actual {
//! [actual]
template <typename T>
struct print_impl : hana::default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
template <typename T>
struct Printable
: hana::integral_constant<bool,
!hana::is_default<print_impl<hana::tag_of_t<T>>>::value
>
{ };
//! [actual]
static_assert(!Printable<void>::value, "");
}
int main() { }
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