127 lines
3.4 KiB
C++
127 lines
3.4 KiB
C++
/*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/.
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*
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* Copyright 2011-2019 Danny Robson <danny@nerdcruft.net>
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*/
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#pragma once
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#include <cstdint>
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#include <cstdlib>
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#include <memory>
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#include <stdexcept>
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#include <tuple>
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///////////////////////////////////////////////////////////////////////////////
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// analogue of std::data for use until we get proper c++17 support
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namespace cruft {
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template <typename T>
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auto
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data (T &t)
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{ return t.data (); }
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//-------------------------------------------------------------------------
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template <typename T>
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auto
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data (const T &t)
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{ return t.data (); }
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//-------------------------------------------------------------------------
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template <typename T, size_t N>
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constexpr T*
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data (T (&t)[N])
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{ return &t[0]; }
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//-------------------------------------------------------------------------
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template <typename T, size_t N>
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constexpr const T*
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data (const T (&t)[N])
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{ return &t[0]; }
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}
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///////////////////////////////////////////////////////////////////////////////
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/// returns the first argument from a parameter pack which can evaluate to true.
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template <class T>
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T
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first (T a)
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{
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if (a)
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return a;
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throw std::logic_error ("no valid object");
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}
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//-----------------------------------------------------------------------------
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template <class T, class ...Args>
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T
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first (T a, Args&& ...b)
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{
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if (a)
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return a;
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return first (std::forward<Args>(b)...);
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}
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namespace cruft {
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///------------------------------------------------------------------------
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/// represents a type as a POD struct (but is statically recoverable via
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/// the 'type' member).
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template <typename T>
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struct type_tag
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{
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typedef T type;
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};
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///------------------------------------------------------------------------
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/// count the number of parameters we are given. useful for counting
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/// arguments in variadic macros (ie, sizeof... (__VA_ARGS__))
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template <typename ...T>
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constexpr size_t
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param_count (const T... t)
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{
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// prevent unused variable warnings by never forwarding recursively
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// ideally we'd use void casting, but it doesn't work for parameter
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// packs
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if (false)
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return param_count (t...);
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return sizeof... (t);
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}
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///////////////////////////////////////////////////////////////////////////
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/// A trait that tests for the presence of a 'native' member function.
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///
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/// Not terrifically useful by itself, but it is use reasonably frequently
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/// in various library wrappers that we maintain (to return the underlying
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/// native objects).
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template <typename ValueT, typename = std::void_t<>>
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struct has_native : public std::false_type
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{};
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//-------------------------------------------------------------------------
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template <
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typename ValueT
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> struct has_native<
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ValueT,
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std::void_t<
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decltype(std::declval<ValueT> ().native ())
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>
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> : public std::true_type {};
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//-------------------------------------------------------------------------
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template <typename ValueT>
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constexpr auto has_native_v = has_native<ValueT>::value;
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}
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