lazyinitializer.h

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/**********************************************************************
 * LeechCraft - modular cross-platform feature rich internet client.
 * Copyright (C) 2006-2014  Georg Rudoy
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE or copy at https://www.boost.org/LICENSE_1_0.txt)
 **********************************************************************/
 
#pragma once
 
#include <functional>
#include <optional>
 
namespace LC
{
namespace Util
{
    template<typename Source, typename Object>
    class LazyInitializer
    {
        Source Source_;
 
        std::optional<Object> Object_;
 
        std::function<Object (Source)> Initializer_;
        std::function<void (Source&)> ClearSource_;
    public:
        template<typename Init>
        LazyInitializer (const Source& source,
                const Init& initializer,
                const std::function<void (Source&)>& clear = [] (Source& src) { src = Source {}; })
        : Source_ { source }
        , Initializer_ { initializer }
        , ClearSource_ { clear }
        {
        }
 
        LazyInitializer (const Object& object)
        : Object_ { object }
        {
        }
 
        LazyInitializer& operator= (const Object& object)
        {
            Object_ = object;
            ClearSource_ (Source_);
            return *this;
        }
 
        operator Object ()
        {
            CheckInit ();
            return *Object_;
        }
 
        Object& operator-> ()
        {
            CheckInit ();
            return *Object_;
        }
 
        void Force ()
        {
            CheckInit ();
        }
    private:
        void CheckInit ()
        {
            if (!Object_)
            {
                Object_ = Initializer_ (Source_);
                ClearSource_ (Source_);
            }
        }
    };
}
}