First blush
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MultiMethods.h
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MultiMethods.h
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////////////////////////////////////////////////////////////////////////////////
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// The Loki Library
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// Copyright (c) 2001 by Andrei Alexandrescu
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// This code accompanies the book:
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// Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design
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// Patterns Applied". Copyright (c) 2001. Addison-Wesley.
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// Permission to use, copy, modify, distribute and sell this software for any
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// purpose is hereby granted without fee, provided that the above copyright
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// notice appear in all copies and that both that copyright notice and this
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// permission notice appear in supporting documentation.
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// The author or Addison-Welsey Longman make no representations about the
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// suitability of this software for any purpose. It is provided "as is"
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// without express or implied warranty.
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////////////////////////////////////////////////////////////////////////////////
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// Last update: February 19, 2001
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#ifndef MULTIMETHODS_INC_
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#define MULTIMETHODS_INC_
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#include "Typelist.h"
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#include "TypeInfo.h"
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#include "Functor.h"
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#include "AssocVector.h"
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////////////////////////////////////////////////////////////////////////////////
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// IMPORTANT NOTE:
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// The double dispatchers implemented below differ from the excerpts shown in
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// the book - they are simpler while respecting the same interface.
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////////////////////////////////////////////////////////////////////////////////
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namespace Loki
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{
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////////////////////////////////////////////////////////////////////////////////
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// class template InvocationTraits (helper)
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// Helps implementing optional symmetry
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////////////////////////////////////////////////////////////////////////////////
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namespace Private
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{
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template <bool swapArgs, class SomeLhs, class SomeRhs, class Executor,
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typename ResultType>
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struct InvocationTraits
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{
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static ResultType DoDispatch(SomeLhs& lhs, SomeRhs& rhs,
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Executor& exec)
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{
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return exec.Fire(lhs, rhs);
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}
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};
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template <class SomeLhs, class SomeRhs, class Executor,
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typename ResultType>
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struct InvocationTraits<true, SomeLhs, SomeRhs, Executor, ResultType>
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{
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static ResultType DoDispatch(SomeLhs& lhs, SomeRhs& rhs,
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Executor& exec)
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{
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return exec.Fire(rhs, lhs); // swap arguments
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}
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};
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}
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////////////////////////////////////////////////////////////////////////////////
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// class template StaticDispatcher
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// Implements an automatic static double dispatcher based on two typelists
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////////////////////////////////////////////////////////////////////////////////
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template
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<
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class Executor,
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bool symmetric,
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class BaseLhs,
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class TypesLhs,
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class BaseRhs = BaseLhs,
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class TypesRhs = TypesLhs,
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typename ResultType = void
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>
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class StaticDispatcher
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{
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template <class SomeLhs>
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static ResultType DispatchRhs(SomeLhs& lhs, BaseRhs& rhs,
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Executor exec, NullType)
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{ return exec.OnError(lhs, rhs); }
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template <class TList, class SomeLhs>
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static ResultType DispatchRhs(SomeLhs& lhs, BaseRhs& rhs,
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Executor exec, TList)
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{
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typedef typename TList::Head Head;
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typedef typename TList::Tail Tail;
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if (Head* p2 = dynamic_cast<Head*>(&rhs))
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{
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enum { swapArgs = symmetric &&
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TL::IndexOf<TypesRhs, Head>::value <
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TL::IndexOf<TypesLhs, SomeLhs>::value };
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typedef Private::InvocationTraits<swapArgs,
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SomeLhs, Head, Executor, ResultType>
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CallTraits;
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return CallTraits::DoDispatch(lhs, *p2, exec);
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}
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return DispatchRhs(lhs, rhs, exec, Tail());
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}
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static ResultType DispatchLhs(BaseLhs& lhs, BaseRhs& rhs,
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Executor exec, NullType)
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{ return exec.OnError(lhs, rhs); }
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template <class TList>
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static ResultType DispatchLhs(BaseLhs& lhs, BaseRhs& rhs,
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Executor exec, TList)
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{
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typedef typename TList::Head Head;
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typedef typename TList::Tail Tail;
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if (Head* p1 = dynamic_cast<Head*>(&lhs))
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{
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return DispatchRhs(*p1, rhs, exec, TypesRhs());
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}
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return DispatchLhs(lhs, rhs, exec, Tail());
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}
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public:
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static ResultType Go(BaseLhs& lhs, BaseRhs& rhs,
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Executor exec)
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{ return DispatchLhs(lhs, rhs, exec, TypesLhs()); }
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template BasicDispatcher
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// Implements a logarithmic double dispatcher for functors (or functions)
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// Doesn't offer automated casts or symmetry
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////////////////////////////////////////////////////////////////////////////////
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template
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<
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class BaseLhs,
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class BaseRhs = BaseLhs,
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typename ResultType = void,
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typename CallbackType = ResultType (*)(BaseLhs&, BaseRhs&)
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>
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class BasicDispatcher
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{
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typedef std::pair<TypeInfo, TypeInfo> KeyType;
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typedef CallbackType MappedType;
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typedef AssocVector<KeyType, MappedType> MapType;
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MapType callbackMap_;
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public:
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void DoAdd(TypeInfo lhs, TypeInfo rhs, CallbackType fun)
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{
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callbackMap_[KeyType(lhs, rhs)] = fun;
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}
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bool DoRemove(TypeInfo lhs, TypeInfo rhs)
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{
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return callbackMap_.erase(KeyType(lhs, rhs)) == 1;
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}
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template <class SomeLhs, class SomeRhs>
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void Add(CallbackType fun)
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{
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DoAdd(typeid(SomeLhs), typeid(SomeRhs), fun);
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}
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template <class SomeLhs, class SomeRhs>
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bool Remove()
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{
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return DoRemove(typeid(SomeLhs), typeid(SomeRhs));
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}
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ResultType Go(BaseLhs& lhs, BaseRhs& rhs)
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{
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MapType::iterator i = callbackMap_.find(
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KeyType(typeid(lhs), typeid(rhs)));
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if (i == callbackMap_.end())
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{
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throw std::runtime_error("Function not found");
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}
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return (i->second)(lhs, rhs);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template StaticCaster
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// Implementation of the CastingPolicy used by FunctorDispatcher
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////////////////////////////////////////////////////////////////////////////////
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template <class To, class From>
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struct StaticCaster
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{
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static To& Cast(From& obj)
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{
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return static_cast<To&>(obj);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template DynamicCaster
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// Implementation of the CastingPolicy used by FunctorDispatcher
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////////////////////////////////////////////////////////////////////////////////
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template <class To, class From>
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struct DynamicCaster
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{
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static To& Cast(From& obj)
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{
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return dynamic_cast<To&>(obj);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template FnDispatcher
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// Implements an automatic logarithmic double dispatcher for functions
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// Features automated conversions
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////////////////////////////////////////////////////////////////////////////////
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template <class BaseLhs, class BaseRhs = BaseLhs,
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typename ResultType = void,
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template <class, class> class CastingPolicy = DynamicCaster,
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template <class, class, class, class>
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class DispatcherBackend = BasicDispatcher>
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class FnDispatcher
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{
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DispatcherBackend<BaseLhs, BaseRhs, ResultType,
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ResultType (*)(BaseLhs&, BaseRhs&)> backEnd_;
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public:
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template <class ConcreteLhs, class ConcreteRhs>
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void Add(ResultType (*pFun)(BaseLhs&, BaseRhs&))
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{
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return backEnd_.Add<ConcreteLhs, ConcreteRhs>(pFun);
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}
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template <class ConcreteLhs, class ConcreteRhs,
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ResultType (*callback)(ConcreteLhs&, ConcreteRhs&),
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bool symmetric>
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void Add()
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{
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struct Local
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{
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static ResultType Trampoline(BaseLhs& lhs, BaseRhs& rhs)
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{
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return callback(
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CastingPolicy<ConcreteLhs, BaseLhs>::Cast(lhs),
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CastingPolicy<ConcreteRhs, BaseRhs>::Cast(rhs));
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}
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static ResultType TrampolineR(BaseRhs& rhs, BaseLhs& lhs)
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{
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return Trampoline(lhs, rhs);
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}
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};
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Add<ConcreteLhs, ConcreteRhs>(&Local::Trampoline);
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if (symmetric)
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{
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Add<ConcreteRhs, ConcreteLhs>(&Local::TrampolineR);
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}
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}
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ResultType Go(BaseLhs& lhs, BaseRhs& rhs)
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{
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return backEnd_.Go(lhs, rhs);
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}
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};
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////////////////////////////////////////////////////////////////////////////////
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// class template FunctorDispatcher
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// Implements a logarithmic double dispatcher for functors
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// Features automated casting
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////////////////////////////////////////////////////////////////////////////////
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template <class BaseLhs, class BaseRhs = BaseLhs,
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typename ResultType = void,
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template <class, class> class CastingPolicy = DynamicCaster,
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template <class, class, class, class>
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class DispatcherBackend = BasicDispatcher>
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class FunctorDispatcher
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{
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typedef TYPELIST_2(BaseLhs&, BaseRhs&) ArgsList;
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typedef Functor<ResultType, ArgsList, DEFAULT_THREADING> FunctorType;
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typedef DispatcherBackend<BaseLhs, BaseRhs, ResultType, FunctorType>
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BackEndType;
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BackEndType backEnd_;
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public:
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template <class SomeLhs, class SomeRhs, class Fun>
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void Add(const Fun& fun)
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{
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typedef FunctorImpl<ResultType, TYPELIST_2(BaseLhs, BaseRhs)>
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FunctorImplType;
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class Adapter : public FunctorImplType
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{
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Fun fun_;
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virtual ResultType operator()(BaseLhs& lhs, BaseRhs& rhs)
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{
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return fun_(
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CastingPolicy<ConcreteLhs, BaseLhs>::Cast(lhs),
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CastingPolicy<ConcreteRhs, BaseRhs>::Cast(rhs));
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}
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virtual FunctorImplType* DoClone() const
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{ return new Adapter(*this); }
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public:
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Adapter(const Fun& fun) : fun_(fun) {}
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};
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backEnd_.Add<SomeLhs, SomeRhs>(
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Functor<ResultType, ArgsList, DEFAULT_THREADING>(new Adapter(fun)));
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}
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ResultType Go(BaseLhs& lhs, BaseRhs& rhs)
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{
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return backEnd_.Go(lhs, rhs);
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}
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};
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} // namespace Loki
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#endif
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