libcruft-util/types.hpp

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/*
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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
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*
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* 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.
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*
* Copyright 2011-2014 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef __UTIL_TYPES_HPP
#define __UTIL_TYPES_HPP
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#include <cstdint>
#include <cstdlib>
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#include <memory>
#include <stdexcept>
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//-----------------------------------------------------------------------------
/// Returns the number of elements of a statically allocated array
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template <typename T, size_t N>
constexpr size_t
elems (const T (&)[N])
{ return N; }
template <typename T>
constexpr typename T::size_type
elems (const T &t)
{ return t.size (); }
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///////////////////////////////////////////////////////////////////////////////
// analogue of std::data for use until we get proper c++17 support
namespace util {
template <typename T>
auto
data (T &t)
{ return t.data (); }
//-------------------------------------------------------------------------
template <typename T>
auto
data (const T &t)
{ return t.data (); }
//-------------------------------------------------------------------------
template <typename T, size_t N>
constexpr T*
data (T (&t)[N])
{ return &t[0]; }
//-------------------------------------------------------------------------
template <typename T, size_t N>
constexpr const T*
data (const T (&t)[N])
{ return &t[0]; }
}
///////////////////////////////////////////////////////////////////////////////
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/// returns the first argument from a parameter pack which can evaluate to true.
template <class T>
T
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first (T a)
{
if (a)
return a;
throw std::logic_error ("no valid object");
}
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//-----------------------------------------------------------------------------
template <class T, class ...Args>
T
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first (T a, Args&& ...b)
{
if (a)
return a;
return first (std::forward<Args>(b)...);
}
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namespace util {
///------------------------------------------------------------------------
/// represents a type as a POD struct (but is statically recoverable via
/// the 'type' member).
template <typename T>
struct type_tag
{
typedef T type;
};
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///------------------------------------------------------------------------
/// count the number of parameters we are given. useful for counting
/// arguments in variadic macros (ie, sizeof... (__VA_ARGS__))
template <typename ...T>
constexpr size_t
param_count (const T... t)
{
// prevent unused variable warnings by never forwarding recursively
// ideally we'd use void casting, but it doesn't work for parameter
// packs
if (false)
return param_count (t...);
return sizeof... (t);
}
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}
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#endif