78 lines
2.3 KiB
C++
78 lines
2.3 KiB
C++
/* This file is part of Clementine.
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Copyright 2016, John Maguire <john.maguire@gmail.com>
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Clementine is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Clementine is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Clementine. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef LAZY_H
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#define LAZY_H
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#include <functional>
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#include <memory>
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// Helper for lazy initialisation of objects.
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// Usage1:
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// Lazy<Foo> my_lazy_object([]() { return new Foo; });
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// Usage2:
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// Lazy<Foo> my_lazy_object([]() { return new Foo; },
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// [](Foo *foo) { delete foo; });
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// Note: the Lazy::default_deleter just deletes the object. The default
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// unique_ptr would have a specialization for arrays. The second usage
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// should be used with arrays.
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//
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template <typename T>
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class Lazy {
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public:
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explicit Lazy(std::function<T*()> init,
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std::function<void(T*)> deleter = Lazy::default_deleter)
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: init_(init), ptr_(nullptr, deleter) {}
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// Convenience constructor that will lazily default construct the object.
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Lazy()
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: init_([]() { return new T; }), ptr_(nullptr, Lazy::default_deleter) {}
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T* get() const {
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CheckInitialised();
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return ptr_.get();
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}
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typename std::add_lvalue_reference<T>::type operator*() const {
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CheckInitialised();
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return *ptr_;
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}
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T* operator->() const { return get(); }
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// Returns true if the object is not yet initialised.
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explicit operator bool() const { return ptr_; }
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// Deletes the underlying object and will re-run the initialisation function
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// if the object is requested again.
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void reset() { ptr_.reset(nullptr); }
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static void default_deleter(T* obj) { delete obj; }
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private:
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void CheckInitialised() const {
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if (!ptr_) {
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ptr_.reset(init_());
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}
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}
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const std::function<T*()> init_;
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mutable std::unique_ptr<T, std::function<void(T*)>> ptr_;
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};
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#endif // LAZY_H
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