smartptr.h

《C++设计新思维》中的Loki源代码。其中把template用到了极致。

        static P Clone(const P&)
        {
            // Make it depended on template parameter
            static const bool DependedFalse = sizeof(P*) == 0;

            STATIC_CHECK(DependedFalse, This_Policy_Disallows_Value_Copying);
        }
        
        static bool Release(const P&)
        { return true; }
        
        static void Swap(NoCopy&)
        {}
        
        enum { destructiveCopy = false };
    };
    
////////////////////////////////////////////////////////////////////////////////
// class template AllowConversion
// Implementation of the ConversionPolicy used by SmartPtr
// Allows implicit conversion from SmartPtr to the pointee type
////////////////////////////////////////////////////////////////////////////////

    struct AllowConversion
    {
        enum { allow = true };

        void Swap(AllowConversion&)
        {}
    };

////////////////////////////////////////////////////////////////////////////////
// class template DisallowConversion
// Implementation of the ConversionPolicy used by SmartPtr
// Does not allow implicit conversion from SmartPtr to the pointee type
// You can initialize a DisallowConversion with an AllowConversion
////////////////////////////////////////////////////////////////////////////////

    struct DisallowConversion
    {
        DisallowConversion()
        {}
        
        DisallowConversion(const AllowConversion&)
        {}
        
        enum { allow = false };

        void Swap(DisallowConversion&)
        {}
    };

////////////////////////////////////////////////////////////////////////////////
// class template NoCheck
// Implementation of the CheckingPolicy used by SmartPtr
// Well, it's clear what it does :o)
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct NoCheck
    {
        NoCheck()
        {}
        
        template <class P1>
        NoCheck(const NoCheck<P1>&)
        {}
        
        static void OnDefault(const P&)
        {}

        static void OnInit(const P&)
        {}

        static void OnDereference(const P&)
        {}

        static void Swap(NoCheck&)
        {}
    };


////////////////////////////////////////////////////////////////////////////////
// class template AssertCheck
// Implementation of the CheckingPolicy used by SmartPtr
// Checks the pointer before dereference
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct AssertCheck
    {
        AssertCheck()
        {}
        
        template <class P1>
        AssertCheck(const AssertCheck<P1>&)
        {}
        
        template <class P1>
        AssertCheck(const NoCheck<P1>&)
        {}
        
        static void OnDefault(const P&)
        {}

        static void OnInit(const P&)
        {}

        static void OnDereference(P val)
        { assert(val); (void)val; }

        static void Swap(AssertCheck&)
        {}
    };

////////////////////////////////////////////////////////////////////////////////
// class template AssertCheckStrict
// Implementation of the CheckingPolicy used by SmartPtr
// Checks the pointer against zero upon initialization and before dereference
// You can initialize an AssertCheckStrict with an AssertCheck 
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct AssertCheckStrict
    {
        AssertCheckStrict()
        {}
        
        template <class U>
        AssertCheckStrict(const AssertCheckStrict<U>&)
        {}
        
        template <class U>
        AssertCheckStrict(const AssertCheck<U>&)
        {}
        
        template <class P1>
        AssertCheckStrict(const NoCheck<P1>&)
        {}
        
        static void OnDefault(P val)
        { assert(val); }
        
        static void OnInit(P val)
        { assert(val); }
        
        static void OnDereference(P val)
        { assert(val); }
        
        static void Swap(AssertCheckStrict&)
        {}
    };

////////////////////////////////////////////////////////////////////////////////
// class NullPointerException
// Used by some implementations of the CheckingPolicy used by SmartPtr
////////////////////////////////////////////////////////////////////////////////

    struct NullPointerException : public std::runtime_error
    {
        NullPointerException() : std::runtime_error("")
        { }
        const char* what() const throw()
        { return "Null Pointer Exception"; }
    };
        
////////////////////////////////////////////////////////////////////////////////
// class template RejectNullStatic
// Implementation of the CheckingPolicy used by SmartPtr
// Checks the pointer upon initialization and before dereference
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct RejectNullStatic
    {
        RejectNullStatic()
        {}
        
        template <class P1>
        RejectNullStatic(const RejectNullStatic<P1>&)
        {}
        
        template <class P1>
        RejectNullStatic(const NoCheck<P1>&)
        {}
        
        template <class P1>
        RejectNullStatic(const AssertCheck<P1>&)
        {}
        
        template <class P1>
        RejectNullStatic(const AssertCheckStrict<P1>&)
        {}
        
        static void OnDefault(const P&)
        {
            // Make it depended on template parameter
            static const bool DependedFalse = sizeof(P*) == 0;

            STATIC_CHECK(DependedFalse, ERROR_This_Policy_Does_Not_Allow_Default_Initialization);
        }
        
        static void OnInit(const P& val)
        { if (!val) throw NullPointerException(); }
        
        static void OnDereference(const P& val)
        { if (!val) throw NullPointerException(); }
        
        static void Swap(RejectNullStatic&)
        {}
    };

////////////////////////////////////////////////////////////////////////////////
// class template RejectNull
// Implementation of the CheckingPolicy used by SmartPtr
// Checks the pointer before dereference
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct RejectNull
    {
        RejectNull()
        {}
        
        template <class P1>
        RejectNull(const RejectNull<P1>&)
        {}
        
        static void OnInit(P val)
        { if (!val) throw NullPointerException(); }

        static void OnDefault(P val)
        { OnInit(val); }
        
        void OnDereference(P val)
        { OnInit(val); }
        
        void Swap(RejectNull&)
        {}        
    };

////////////////////////////////////////////////////////////////////////////////
// class template RejectNullStrict
// Implementation of the CheckingPolicy used by SmartPtr
// Checks the pointer upon initialization and before dereference
////////////////////////////////////////////////////////////////////////////////

    template <class P>
    struct RejectNullStrict
    {
        RejectNullStrict()
        {}
        
        template <class P1>
        RejectNullStrict(const RejectNullStrict<P1>&)
        {}
        
        template <class P1>
        RejectNullStrict(const RejectNull<P1>&)
        {}
        
        static void OnInit(P val)
        { if (!val) throw NullPointerException(); }

        void OnDereference(P val)
        { OnInit(val); }
        
        void Swap(RejectNullStrict&)
        {}        
    };

////////////////////////////////////////////////////////////////////////////////
// class template ByRef
// Transports a reference as a value
// Serves to implement the Colvin/Gibbons trick for SmartPtr
////////////////////////////////////////////////////////////////////////////////

    template <class T>
    class ByRef
    {
    public:
        ByRef(T& v) : value_(v) {}
        operator T&() { return value_; }
        // gcc doesn't like this:
        // operator const T&() const { return value_; }
    private:
        ByRef& operator=(const ByRef &);
        T& value_;
    };

////////////////////////////////////////////////////////////////////////////////
// class template SmartPtr (declaration)
// The reason for all the fuss above
////////////////////////////////////////////////////////////////////////////////

    template
    <
        typename T,
        template <class> class OwnershipPolicy = RefCounted,
        class ConversionPolicy = DisallowConversion,
        template <class> class CheckingPolicy = AssertCheck,
        template <class> class StoragePolicy = DefaultSPStorage
    >
    class SmartPtr;

////////////////////////////////////////////////////////////////////////////////
// class template SmartPtrDef (definition)
// this class added to unify the usage of SmartPtr 
// instead of writing SmartPtr<T,OP,CP,KP,SP> write SmartPtrDef<T,OP,CP,KP,SP>::type
////////////////////////////////////////////////////////////////////////////////

    template
    <
        typename T,
        template <class> class OwnershipPolicy = RefCounted,
        class ConversionPolicy = DisallowConversion,
        template <class> class CheckingPolicy = AssertCheck,
        template <class> class StoragePolicy = DefaultSPStorage
    >
    struct SmartPtrDef
    {
        typedef SmartPtr
        <
            T,
            OwnershipPolicy,
            ConversionPolicy,
            CheckingPolicy,
            StoragePolicy
        >
        type;
    };

////////////////////////////////////////////////////////////////////////////////
// class template SmartPtr (definition)
////////////////////////////////////////////////////////////////////////////////

    template
    <
        typename T,
        template <class> class OwnershipPolicy,
        class ConversionPolicy,
        template <class> class CheckingPolicy,
        template <class> class StoragePolicy
    >
    class SmartPtr
        : public StoragePolicy<T>
        , public OwnershipPolicy<typename StoragePolicy<T>::PointerType>
        , public CheckingPolicy<typename StoragePolicy<T>::StoredType>
        , public ConversionPolicy
    {
        typedef StoragePolicy<T> SP;
        typedef OwnershipPolicy<typename StoragePolicy<T>::PointerType> OP;
        typedef CheckingPolicy<typename StoragePolicy<T>::StoredType> KP;
        typedef ConversionPolicy CP;
        
    public:
        typedef typename SP::PointerType PointerType;
        typedef typename SP::StoredType StoredType;
        typedef typename SP::ReferenceType ReferenceType;
        
        typedef typename Select<OP::destructiveCopy, 
                SmartPtr, const SmartPtr>::Result
            CopyArg;
    
    private:
        struct NeverMatched;
       
#ifdef LOKI_SMARTPTR_CONVERSION_CONSTRUCTOR_POLICY
        typedef typename Select< CP::allow, const StoredType&, NeverMatched>::Result ImplicitArg;
        typedef typename Select<!CP::allow, const StoredType&, NeverMatched>::Result ExplicitArg;
#else
        typedef const StoredType& ImplicitArg;
        typedef typename Select<false, const StoredType&, NeverMatched>::Result ExplicitArg;
#endif

    public:

        SmartPtr()
        { KP::OnDefault(GetImpl(*this)); }
        
        explicit
        SmartPtr(ExplicitArg p) : SP(p)
        { KP::OnInit(GetImpl(*this)); }

        SmartPtr(ImplicitArg p) : SP(p)
        { KP::OnInit(GetImpl(*this)); }

        SmartPtr(CopyArg& rhs)
        : SP(rhs), OP(rhs), KP(rhs), CP(rhs)
        { GetImplRef(*this) = OP::Clone(GetImplRef(rhs)); }

        template
        <
            typename T1,
            template <class> class OP1,
            class CP1,
            template <class> class KP1,
            template <class> class SP1
        >
        SmartPtr(const SmartPtr<T1, OP1, CP1, KP1, SP1>& rhs)
        : SP(rhs), OP(rhs), KP(rhs), CP(rhs)
        { GetImplRef(*this) = OP::Clone(GetImplRef(rhs)); }

        template
        <
            typename T1,
            template <class> class OP1,
            class CP1,
            template <class> class KP1,
            template <class> class SP1
        >
        SmartPtr(SmartPtr<T1, OP1, CP1, KP1, SP1>& rhs)
        : SP(rhs), OP(rhs), KP(rhs), CP(rhs)
        { GetImplRef(*this) = OP::Clone(GetImplRef(rhs)); }

        SmartPtr(ByRef<SmartPtr> rhs)
        : SP(rhs), OP(rhs), KP(rhs), CP(rhs)