deferred_construction_ptr.hh

00001 /* vim: set sw=4 sts=4 et foldmethod=syntax : */
00002 
00003 /*
00004  * Copyright (c) 2008 Ciaran McCreesh
00005  *
00006  * This file is part of the Paludis package manager. Paludis is free software;
00007  * you can redistribute it and/or modify it under the terms of the GNU General
00008  * Public License version 2, as published by the Free Software Foundation.
00009  *
00010  * Paludis is distributed in the hope that it will be useful, but WITHOUT ANY
00011  * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
00012  * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
00013  * details.
00014  *
00015  * You should have received a copy of the GNU General Public License along with
00016  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
00017  * Place, Suite 330, Boston, MA  02111-1307  USA
00018  */
00019 
00020 #ifndef PALUDIS_GUARD_PALUDIS_UTIL_DEFERRED_CONSTRUCTION_PTR_HH
00021 #define PALUDIS_GUARD_PALUDIS_UTIL_DEFERRED_CONSTRUCTION_PTR_HH 1
00022 
00023 #include <paludis/util/deferred_construction_ptr-fwd.hh>
00024 #include <tr1/functional>
00025 
00026 namespace paludis
00027 {
00028     template <typename T_>
00029     class DeferredConstructionPtr
00030     {
00031         private:
00032             mutable T_ _ptr;
00033             std::tr1::function<T_ ()> _f;
00034             mutable bool _done;
00035 
00036         public:
00037             DeferredConstructionPtr(const std::tr1::function<T_ ()> & f) :
00038                 _ptr(),
00039                 _f(f),
00040                 _done(false)
00041             {
00042             }
00043 
00044             DeferredConstructionPtr(const DeferredConstructionPtr & other) :
00045                 _ptr(other._ptr),
00046                 _f(other._f),
00047                 _done(other._done)
00048             {
00049             }
00050 
00051             DeferredConstructionPtr &
00052             operator= (const DeferredConstructionPtr & other)
00053             {
00054                 if (this != &other)
00055                 {
00056                     _ptr = other._ptr;
00057                     _f = other._f;
00058                     _done = other._done;
00059                 }
00060                 return *this;
00061             }
00062 
00063             T_ operator-> () const
00064             {
00065                 if (! _done)
00066                 {
00067                     _ptr = _f();
00068                     _done = true;
00069                 }
00070 
00071                 return _ptr;
00072             }
00073     };
00074 }
00075 
00076 #endif

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