strawberry-audio-player-win.../src/core/lazy.h

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/* This file is part of Strawberry.
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Copyright 2016, John Maguire <john.maguire@gmail.com>
Strawberry 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
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Strawberry is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Strawberry. If not, see <http://www.gnu.org/licenses/>.
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*/
#ifndef LAZY_H
#define LAZY_H
#include <functional>
#include <memory>
// Helper for lazy initialization of objects.
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// Usage:
// Lazy<Foo> my_lazy_object([]() { return new Foo; });
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template<typename T>
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class Lazy {
public:
explicit Lazy(std::function<T*()> init) : init_(init) {}
// Convenience constructor that will lazily default construct the object.
Lazy() : init_([]() { return new T; }) {}
T* get() const {
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CheckInitialized();
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return ptr_.get();
}
typename std::add_lvalue_reference<T>::type operator*() const {
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CheckInitialized();
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return *ptr_;
}
T* operator->() const { return get(); }
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// Returns true if the object is not yet initialized.
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explicit operator bool() const { return ptr_; }
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// Deletes the underlying object and will re-run the initialization function if the object is requested again.
void reset() { ptr_.reset(); }
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private:
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void CheckInitialized() const {
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if (!ptr_) {
ptr_.reset(init_(), [](T*obj) { obj->deleteLater(); });
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}
}
const std::function<T*()> init_;
mutable std::shared_ptr<T> ptr_;
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};
#endif // LAZY_H