First blush

git-svn-id: svn://svn.code.sf.net/p/loki-lib/code/trunk@6 7ec92016-0320-0410-acc4-a06ded1c099a

TypeManip.h

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+////////////////////////////////////////////////////////////////////////////////
+// The Loki Library
+// Copyright (c) 2001 by Andrei Alexandrescu
+// This code accompanies the book:
+// Alexandrescu, Andrei. "Modern C++ Design: Generic Programming and Design 
+//     Patterns Applied". Copyright (c) 2001. Addison-Wesley.
+// Permission to use, copy, modify, distribute and sell this software for any 
+//     purpose is hereby granted without fee, provided that the above copyright 
+//     notice appear in all copies and that both that copyright notice and this 
+//     permission notice appear in supporting documentation.
+// The author or Addison-Welsey Longman make no representations about the 
+//     suitability of this software for any purpose. It is provided "as is" 
+//     without express or implied warranty.
+////////////////////////////////////////////////////////////////////////////////
+
+// Last update: February 19, 2001
+
+#ifndef TYPEMANIP_INC_
+#define TYPEMANIP_INC_
+
+namespace Loki
+{
+////////////////////////////////////////////////////////////////////////////////
+// class template Int2Type
+// Converts each integral constant into a unique type
+// Invocation: Int2Type<v> where v is a compile-time constant integral
+// Defines 'value', an enum that evaluates to v
+////////////////////////////////////////////////////////////////////////////////
+
+    template <int v>
+    struct Int2Type
+    {
+        enum { value = v };
+    };
+    
+////////////////////////////////////////////////////////////////////////////////
+// class template Type2Type
+// Converts each type into a unique, insipid type
+// Invocation Type2Type<T> where T is a type
+// Defines the type OriginalType which maps back to T
+////////////////////////////////////////////////////////////////////////////////
+
+    template <typename T>
+    struct Type2Type
+    {
+        typedef T OriginalType;
+    };
+    
+////////////////////////////////////////////////////////////////////////////////
+// class template Select
+// Selects one of two types based upon a boolean constant
+// Invocation: Select<flag, T, U>::Result
+// where:
+// flag is a compile-time boolean constant
+// T and U are types
+// Result evaluates to T if flag is true, and to U otherwise.
+////////////////////////////////////////////////////////////////////////////////
+
+    template <bool flag, typename T, typename U>
+    struct Select
+    {
+        typedef T Result;
+    };
+    template <typename T, typename U>
+    struct Select<false, T, U>
+    {
+        typedef U Result;
+    };
+    
+////////////////////////////////////////////////////////////////////////////////
+// Helper types Small and Big - guarantee that sizeof(Small) < sizeof(Big)
+////////////////////////////////////////////////////////////////////////////////
+
+    namespace Private
+    {
+        typedef char Small;
+        class Big { char dummy[2]; };
+    }
+
+////////////////////////////////////////////////////////////////////////////////
+// class template Conversion
+// Figures out the conversion relationships between two types
+// Invocations (T and U are types):
+// a) Conversion<T, U>::exists
+// returns (at compile time) true if there is an implicit conversion from T
+// to U (example: Derived to Base)
+// b) Conversion<T, U>::exists2Way
+// returns (at compile time) true if there are both conversions from T
+// to U and from U to T (example: int to char and back)
+// c) Conversion<T, U>::sameType
+// returns (at compile time) true if T and U represent the same type
+//
+// Caveat: might not work if T and U are in a private inheritance hierarchy.
+////////////////////////////////////////////////////////////////////////////////
+
+    template <class T, class U>
+    class Conversion
+    {
+        static Private::Big Test(...);
+        static Private::Small Test(U);
+        static T MakeT();
+
+    public:
+        enum { exists = sizeof(Test(MakeT())) == sizeof(Private::Small) };
+        enum { exists2Way = exists && 
+            Conversion<U, T>::exists };
+        enum { sameType = false };
+    };
+    
+    template <class T>
+    class Conversion<T, T>    
+    {
+    public:
+        enum { exists = 1, exists2Way = 1,sameType = 1 };
+    };
+    
+    template <class T>
+    class Conversion<void, T>    
+    {
+    public:
+        enum { exists = 1, exists2Way = 0,sameType = 0 };
+    };
+    
+    template <class T>
+    class Conversion<T, void>    
+    {
+    public:
+        enum { exists = 1, exists2Way = 0,sameType = 0 };
+    };
+    
+    template <>
+    class Conversion<void, void>    
+    {
+    public:
+        enum { exists = 1, exists2Way = 1,sameType = 1 };
+    };    
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// macro SUPERSUBCLASS
+// Invocation: SUPERSUBCLASS(B, D) where B and D are types. 
+// Returns true if B is a public base of D, or if B and D are aliases of the 
+// same type.
+//
+// Caveat: might not work if T and U are in a private inheritance hierarchy.
+////////////////////////////////////////////////////////////////////////////////
+
+#define SUPERSUBCLASS(T, U) \
+    (::Loki::Conversion<const U*, const T*>::exists && \
+    !::Loki::Conversion<const T*, const void*>::sameType)
+
+////////////////////////////////////////////////////////////////////////////////
+// macro SUPERSUBCLASS
+// Invocation: SUPERSUBCLASS(B, D) where B and D are types. 
+// Returns true if B is a public base of D.
+//
+// Caveat: might not work if T and U are in a private inheritance hierarchy.
+////////////////////////////////////////////////////////////////////////////////
+
+#define SUPERSUBCLASS_STRICT(T, U) \
+    (SUPERSUBCLASS(T, U) && \
+    !::Loki::Conversion<const T, const U>::sameType)
+
+
+#endif // TYPEMANIP_INC_