libcruft-util/strongdef.hpp

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/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2015 Danny Robson <danny@nerdcruft.net>
*/
#ifndef __UTIL_STRONGDEF_HPP
#define __UTIL_STRONGDEF_HPP
#include <limits>
#include <type_traits>
namespace util {
/// A transparent wrapper around a (typically lightweight) type for the
/// purposes of overload disambiguation. It acts like a typesafe typedef.
template <typename T,typename Tag>
struct strongdef {
public:
using value_type = T;
using tag_type = Tag;
constexpr strongdef () = delete;
constexpr explicit strongdef (const T &_data): data (_data) { ; }
// explicitly disable assignment with unequal types or tags. this
// prevents the converion operator getting invoked and falsely
// allowing assignment with differing types or tags.
template <typename U, typename TagU>
std::enable_if_t<
!std::is_same<T,U>::value || !std::is_same<Tag,TagU>::value,
strongdef<T,Tag>&
>
operator= (const strongdef<U,TagU> &rhs) = delete;
template <typename U, typename TagU>
std::enable_if_t<
std::is_same<T,U>::value && std::is_same<Tag,TagU>::value,
strongdef<T,Tag>&
>
operator= (const strongdef<U,TagU> &rhs)
{ data = rhs.data; return *this; }
// simple value_type assignment.
strongdef& operator= (const T &rhs)&
{ data = rhs; return *this; }
// conversion operators must not be explicit or it defeats the point
// of this class (ease of use, transparency).
operator const T& (void) const& { return data; }
operator T& (void) & { return data; }
// explicitly disable equality with unequal types or tags. this
// prevents the conversion operator getting invoked and falsely
// allowing equality with different types or tags.
template <typename U, typename TagU>
std::enable_if_t<
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!std::is_same<T, U >::value ||
!std::is_same<Tag,TagU>::value,
bool
>
operator== (const strongdef<U,TagU> &rhs) const = delete;
// provide a usable equality for equal types and tags
template <typename U, typename TagU>
constexpr
std::enable_if_t<
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std::is_same<T, U >::value &&
std::is_same<Tag,TagU>::value,
bool
>
operator== (const strongdef<U,TagU> &rhs) const { return data == rhs.data; }
T data;
};
}
namespace std {
template <typename T, typename Tag>
struct numeric_limits<util::strongdef<T,Tag>> {
using value_type = typename util::strongdef<T,Tag>::value_type;
static constexpr bool is_specialized = numeric_limits<value_type>::is_specialized;
static constexpr bool is_signed = numeric_limits<value_type>::is_signed;
static constexpr bool is_integer = numeric_limits<value_type>::is_integer;
static constexpr bool is_exact = numeric_limits<value_type>::is_exact;
static constexpr bool has_infinity = numeric_limits<value_type>::has_infinity;
static constexpr bool has_quiet_NaN = numeric_limits<value_type>::has_quiet_NaN;
static constexpr bool has_signaling_NaN = numeric_limits<value_type>::has_signaling_NaN;
static constexpr bool has_denorm = numeric_limits<value_type>::has_denorm;
static constexpr bool has_denorm_loss = numeric_limits<value_type>::has_denorm_loss;
static constexpr std::float_round_style round_style = numeric_limits<value_type>::round_style;
static constexpr bool is_iec559 = numeric_limits<value_type>::is_iec559;
static constexpr bool is_bounded = numeric_limits<value_type>::is_bounded;
static constexpr bool is_modulo = numeric_limits<value_type>::is_modulo;
static constexpr int digits = numeric_limits<value_type>::digits;
static constexpr int digits10 = numeric_limits<value_type>::digits10;
static constexpr int max_digits10 = numeric_limits<value_type>::max_digits10;
static constexpr int radix = numeric_limits<value_type>::radix;
static constexpr int min_exponent = numeric_limits<value_type>::min_exponent;
static constexpr int min_exponent10 = numeric_limits<value_type>::min_exponent10;
static constexpr int max_exponent = numeric_limits<value_type>::max_exponent;
static constexpr int max_exponent10 = numeric_limits<value_type>::max_exponent10;
static constexpr bool traps = numeric_limits<value_type>::traps;
static constexpr bool tinyness_before = numeric_limits<value_type>::tinyness_before;
static constexpr value_type min (void) { return numeric_limits<value_type>::min (); }
static constexpr value_type lowest (void) { return numeric_limits<value_type>::lowest (); }
static constexpr value_type max (void) { return numeric_limits<value_type>::max (); }
static constexpr value_type epsilon (void) { return numeric_limits<value_type>::epsilon (); }
static constexpr value_type round_error (void) { return numeric_limits<value_type>::round_error (); }
static constexpr value_type infinity (void) { return numeric_limits<value_type>::infinity (); }
static constexpr value_type quiet_NaN (void) { return numeric_limits<value_type>::quiet_NaN (); }
static constexpr value_type signaling_NaN (void) { return numeric_limits<value_type>::signaling_NaN (); }
static constexpr value_type denorm_min (void) { return numeric_limits<value_type>::denorm_min (); }
};
}
#endif