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107 lines
3.3 KiB
C++
107 lines
3.3 KiB
C++
/*
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@copyright Louis Dionne 2014
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#include <boost/hana/core.hpp>
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#include <type_traits>
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namespace hana = boost::hana;
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//////////////////////////////////////////////////////////////////////////////
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// Type class
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//////////////////////////////////////////////////////////////////////////////
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template <typename T>
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struct Typeclass;
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namespace boost { namespace hana {
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template <>
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struct instance<Typeclass> {
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template <typename T, typename Enable = void>
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struct with {
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static constexpr bool has_complimentary = false;
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static constexpr bool has_defaults = false;
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static constexpr bool has_explicit_instance = false;
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};
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};
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template <>
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struct defaults<Typeclass> {
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template <typename T, typename Enable = void>
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struct with : defaults<> {
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static constexpr bool has_complimentary = false;
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static constexpr bool has_defaults = true;
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static constexpr bool has_explicit_instance = false;
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};
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};
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}}
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template <typename T>
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struct Typeclass : hana::instance<Typeclass>::template with<T> { };
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//////////////////////////////////////////////////////////////////////////////
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// Complimentary instance
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//////////////////////////////////////////////////////////////////////////////
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template <typename T>
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struct predicate : std::false_type { };
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namespace boost { namespace hana {
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template <typename T>
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struct instance<Typeclass>::with<T, std::enable_if_t<predicate<T>{}>>
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: defaults<Typeclass>::template with<T>
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{
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static constexpr bool has_complimentary = true;
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};
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}}
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//////////////////////////////////////////////////////////////////////////////
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// Data types
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//////////////////////////////////////////////////////////////////////////////
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struct AugmentedComplimentary;
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struct Complimentary;
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struct NoComplimentary;
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struct SomethingElse;
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template <>
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struct predicate<AugmentedComplimentary> : std::true_type { };
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template <>
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struct predicate<Complimentary> : std::true_type { };
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template <>
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struct Typeclass<AugmentedComplimentary>
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: hana::instance<Typeclass>::with<AugmentedComplimentary>
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{
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static constexpr bool has_explicit_instance = true;
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};
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template <>
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struct Typeclass<NoComplimentary>
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: hana::defaults<Typeclass>::with<NoComplimentary>
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{
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static constexpr bool has_explicit_instance = true;
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};
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int main() {
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static_assert(Typeclass<AugmentedComplimentary>::has_explicit_instance, "");
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static_assert(Typeclass<AugmentedComplimentary>::has_complimentary, "");
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static_assert(Typeclass<AugmentedComplimentary>::has_defaults, "");
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static_assert(!Typeclass<Complimentary>::has_explicit_instance, "");
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static_assert(Typeclass<Complimentary>::has_complimentary, "");
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static_assert(Typeclass<Complimentary>::has_defaults, "");
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static_assert(Typeclass<NoComplimentary>::has_explicit_instance, "");
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static_assert(!Typeclass<NoComplimentary>::has_complimentary, "");
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static_assert(Typeclass<NoComplimentary>::has_defaults, "");
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static_assert(!Typeclass<SomethingElse>::has_explicit_instance, "");
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static_assert(!Typeclass<SomethingElse>::has_complimentary, "");
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static_assert(!Typeclass<SomethingElse>::has_defaults, "");
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}
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