Danny Robson
f6056153e3
This places, at long last, the core library code into the same namespace as the extended library code.
70 lines
1.9 KiB
C++
70 lines
1.9 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 2018 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef CRUFT_UTIL_SINGLETON_HPP
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#define CRUFT_UTIL_SINGLETON_HPP
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#include "debug.hpp"
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#include <memory>
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namespace cruft {
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/// statically stores a single value of the named type.
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///
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/// this does not prevent the instantiation of the named type, but
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/// instead defines a method to refer to a single instance across an
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/// application.
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template <typename SelfT>
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class singleton {
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private:
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singleton () = default;
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static SelfT *instance;
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public:
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/// instantiates the one blessed value of this type.
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///
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/// `instantiate` must be called once and once only before any calls
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/// to `get`. it is not threadsafe. there are some (unsafe)
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/// assertions against multiple instantiations but they may not be
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/// relied upon.
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///
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/// returns a unique_ptr to the value which the caller must store
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/// until it will never be needed again.
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template <typename ...Args>
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static std::unique_ptr<SelfT>
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instantiate [[nodiscard]] (Args &&...args)
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{
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CHECK (!instance);
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auto cookie =std::make_unique<SelfT> (std::forward<Args> (args)...);
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instance = cookie.get ();
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return cookie;
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}
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/// returns a reference to sole instantiated value
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///
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/// `instantiate` must have already been called before `get` is called.
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static SelfT&
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get (void)
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{
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CHECK (instance);
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return *instance;
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}
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};
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};
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template <typename SelfT>
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SelfT*
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cruft::singleton<SelfT>::instance;
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#endif
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