Changeset 1753 for code/branches/core3/src

Timestamp:

Sep 9, 2008, 10:18:39 PM (16 years ago)

Author:

rgrieder

Message:

Updated Convert.h comments and structure.
Added conversion_cast<ToType>(FromType value) and conversion_cast<ToType>(FromType value, ToType fallback)

File:

• code/branches/core3/src/util/Convert.h (modified) (9 diffs)

code/branches/core3/src/util/Convert.h

@@ -39 +39 @@
 #include <string>
 #include <sstream>
-#include <istream>
-#include <boost/static_assert.hpp>
 
 #include "Math.h"
 #include "Debug.h"
-#include "SubString.h"
+
+// Gcc generates warnings when implicitely casting from float to int for instance.
+// This is however exactly what convertValue does, so we need to suppress the warnings.
+// They only occur in when using the ImplicitConversion template.
+#if ORXONOX_COMPILER == ORXONOX_COMPILER_GCC
+#  pragma GCC system_header
+#endif
 
 ///////////////////////////////////
@@ -50 +54 @@
 ///////////////////////////////////
 
-// These conversions exhibit ambiguous << or >> operators when using stringstream
-inline bool explicitConversion(std::string* output, const char input)
-{
-    *output = std::string(input, 1);
-    return true;
-}
-inline bool explicitConversion(std::string* output, const unsigned char input)
-{
-    *output = std::string(input, 1);
-    return true;
-}
-inline bool explicitConversion(char* output, const std::string input)
-{
-    if (input != "")
-        *output = input[0];
-    else
-        *output = '\0';
-    return true;
-}
-inline bool explicitConversion(unsigned char* output, const std::string input)
-{
-    if (input != "")
-        *output = input[0];
-    else
-        *output = '\0';
-    return true;
-}
-
-///////////////////////////
-// Static type detection //
-///////////////////////////
+
+///////////////////////////////////////////////
+// Static detection for conversion functions //
+///////////////////////////////////////////////
 
 /* The idea to use the sizeof() operator on return functions to determine function existance
    is described in 'Moder C++ design' by Alexandrescu (2001). */
 
-//template <int a, int b>
-//struct TemplateDebugger
-//{
-//    static int debug(int c, int d) { return 0; } //BOOST_STATIC_ASSERT(0); }
-//};
-
 namespace conversionTests
 {
-
-    // Two struct with very different sizes
-    struct VerySmallStruct { char dummy[1]; };
-    struct VeryBigStruct   { char dummy[1024]; }; // Big is surely larger than Small, even with alignments
-}
-
-//namespace generalFunctionTemplate
-//{
-    // Keep this function out of conversion namespaces because the compiler gives a general
-    // template in the same namesapace a higher priority than any specialisation.
-    // This function simply accepts anything but has lower priority than specialisations.
-    // It can be identified by the larger return value.
+    // A struct that is guaranteed to be larger than any return type of our conversion functions.
+    // So we simply add all the sizes of the return types plus a little bit more.
+    struct VeryBigStruct
+    {
+        char intSize[sizeof(int)];
+        char issSize[sizeof(std::istringstream)];
+        char ossSize[sizeof(std::ostringstream)];
+        char boolSize[sizeof(bool)];
+        char addingMore[4096]; // just to be sure ;)
+    };
+}
+
+namespace separate_namespace
+{
+    // We want to keep the templates for the convert functions out of global namespace so that there
+    // are no ambiguities. These templates are never used anyway, they only serve to detect whether
+    // there is a global funciton for a specific conversion or not.
+    // Now why not putting this in namespace 'conversionTests'?
+    // I can not tell for sure, but I think there is a bug in msvc 8. It chooses this general template
+    // (if it was in 'conversionTests') over a better fitting function in global namespace.
+    // The solution is to use another namespace and then apply the 'using' directive in 'conversionTests'.
+    // Unfortunately there is a (somewhat documented) bug in msvc 8 that exposes namespace members
+    // globally when applying the 'using' directive in a namespace. And it so happens that the bug is
+    // triggered in this file. This unwanted global exposure hopefully doesn't cause ambiguities.
     template <class AnyToType, class AnyFromType>
     conversionTests::VeryBigStruct explicitConversion(AnyToType* output, const AnyFromType input)
     {
-        // The function is exposed globally because of the "using namespace" in conversionTests.
-        // We have to make sure noboy uses it, so a good compiler error would be nice.
+        // We have to make sure noboy uses it , so a good compiler error would be nice.
         *output = (AnyToType)input; // Do not use this function!
-        //BOOST_STATIC_ASSERT(0); // just to be sure
-                return *(new conversionTests::VeryBigStruct());
-    }
-    //conversionTests::VeryBigStruct explicitConversion(...);
-//}
+        // gcc does some syntax checking anyway. So return a correct value that is not a temporary.
+            return *(new conversionTests::VeryBigStruct());
+    }
+}
 
 namespace conversionTests
 {
-    //using namespace generalFunctionTemplate; // Why in separate namespace? See above
-
-    // This operators simply accept anything but have lower priority than specialisations.
-    // It can be identified by the larger return value.
+    // Part of the msvc hack. See above in the namespace for more explanations.
+    using namespace separate_namespace;
+
+    // These operators simply accept anything but have lower priority than specialisations
+    // or exact-match non-template functions.
+    // They can be identified by the larger return value.
+    // We put these in a seperate namespace to avoid conflicts with ambiguities.
     template <class Any>
     conversionTests::VeryBigStruct operator<<(std::ostream& outstream, const Any anything);
@@ -128 +112 @@
     conversionTests::VeryBigStruct operator>>(std::istream& instream,  const Any anything);
 
-    // checks for implicit conversion
     template <class FromType, class ToType>
     class ImplicitConversion
     {
     private:
-        static VerySmallStruct test(ToType); // only accepts ToType, but is preferred over '...'
-                //template <class AnyType>
-        static VeryBigStruct   test(...);//const AnyType anything);    // accepts anything
+        ImplicitConversion(); ImplicitConversion(const ImplicitConversion&); ~ImplicitConversion();
+        // Gets chosen only if there is an implicit conversion from FromType to ToType.
+        static int test(ToType);
+        // Accepts any argument. Why do we not use a template? The reason is that with templates,
+        // the function above is only taken iff it is an exact type match. But since we want to
+        // check for implicit conversion, we have to use the ellipsis.
+        static VeryBigStruct   test(...);
         static FromType object; // helper object to handle private c'tor and d'tor
     public:
-        enum { exists = sizeof(test(object)) == sizeof(VerySmallStruct) };
-    };
-
-    // checks for explicit conversion with explicitConversion()
-    template <class FromType, class ToType, int asdf>
+        // test(object) has only 'VerySmallStruct' return type iff the compiler doesn't choose test(...)
+        enum { exists = !(sizeof(test(object)) == sizeof(VeryBigStruct)) };
+    };
+
+    template <class FromType, class ToType>
     class ExplicitConversion
     {
     private:
+        ExplicitConversion(); ExplicitConversion(const ExplicitConversion&); ~ExplicitConversion();
         static FromType objectFromType; // helper object to handle private c'tor and d'tor
         static ToType   objectToType;   // helper object to handle private c'tor and d'tor
     public:
-        enum { exists = sizeof(explicitConversion(&objectToType, objectFromType)) == sizeof(VerySmallStruct) };
-        static void test();
-    };
-
-    //template <int asdf>
-    //class ExplicitConversion<float, int, asdf>
-    //{
-    //private:
-    //    static float objectFromType; // helper object to handle private c'tor and d'tor
-    //    static int   objectToType;   // helper object to handle private c'tor and d'tor
-    //public:
-    //    enum { exists = sizeof(explicitConversion(&objectToType, objectFromType)) == sizeof(VerySmallStruct) };
-    //    static void test() { TemplateDebugger<sizeof(explicitConversion(&objectToType, objectFromType)), sizeof(VerySmallStruct)>::debug(1,2); }
-    //};
-
-    // checks for conversion via istringstream
+        enum { exists = !(sizeof(explicitConversion(&objectToType, objectFromType)) == sizeof(VeryBigStruct)) };
+    };
+
     template <class Type>
     class IStringStreamOperator
     {
+        IStringStreamOperator(); IStringStreamOperator(const IStringStreamOperator&); ~IStringStreamOperator();
         static std::istringstream istream_; // helper object to perform the '>>' operation
         static Type object;                 // helper object to handle private c'tor and d'tor
     public:
-        enum { exists = (sizeof(istream_ >> object) < sizeof(VerySmallStruct) + 512) };
-    };
-
-    // checks for conversion via ostringstream
+        enum { exists = !(sizeof(istream_ >> object) == sizeof(VeryBigStruct)) };
+    };
+
     template <class Type>
     class OStringStreamOperator
     {
+        OStringStreamOperator(); OStringStreamOperator(const OStringStreamOperator&); ~OStringStreamOperator();
         static std::ostringstream ostream_; // helper object to perform the '<<' operation
         static Type object;                 // helper object to handle private c'tor and d'tor
     public:
-        enum { exists = (sizeof(ostream_ << object) < sizeof(VerySmallStruct) + 512) };
-    };
-}
-
-// shortcut without namespace
+        enum { exists = !(sizeof(ostream_ << object) == sizeof(VeryBigStruct)) };
+    };
+}
+
+/* Shortcuts because we usually don't have a namespace in util/ but need one here for the conversion tests*/
+
+/**
+@brief
+    Checks for an implicit conversion FromType --> TyType.
+    This also works for user defined conversion operators.
+    Usage: ImplicitConversion<FromType, ToType>::exists
+*/
 template <class FromType, class ToType>
 struct ImplicitConversion
 { enum { exists = conversionTests::ImplicitConversion<FromType, ToType>::exists }; };
 
-// shortcut without namespace
+/**
+@brief
+    Checks for an explicit conversion FromType --> TyType via 'explicConversion()' function.
+    There has to e an exact type match for a success!
+    Usage: ExplicitConversion<FromType, ToType>::exists
+*/
 template <class FromType, class ToType>
 struct ExplicitConversion
-{ enum { exists = conversionTests::ExplicitConversion<FromType, ToType, 4>::exists }; };
-
-// shortcut without namespace
+{ enum { exists = conversionTests::ExplicitConversion<FromType, ToType>::exists }; };
+
+/**
+@brief
+    Checks for an explicit conversion std::string --> TyType via >> operator.
+    There has to e an exact type match for a success!
+    Usage: IStringStreamConversion<FromType, ToType>::exists
+*/
 template <class Type>
 struct IStringStreamOperator
 { enum { exists = conversionTests::IStringStreamOperator<Type>::exists }; };
 
-// shortcut without namespace
+/**
+@brief
+    Checks for an explicit conversion std::string --> TyType via << operator.
+    There has to e an exact type match for a success!
+    Usage: OStringStreamConversion<FromType, ToType>::exists
+*/
 template <class Type>
 struct OStringStreamOperator
@@ -206 +204 @@
 
 
-///////////////////////////////
-// Conversion Template Stuff //
-///////////////////////////////
-
+
+////////////////////////////////////
+//// ACTUAL CONVERSION SEQUENCE ////
+////////////////////////////////////
+/*
+    There is a distinct priority when choosing the right conversion function:
+    Overwrites:
+    1. (Partial) template specialisation of ConverterExplicit::convert
+    2. Global functions explicitConversion(ToType* output, const FromType input)
+    Fallbacks:
+    3. Any possible implicit conversion. This includes FooBar --> int if FooBar defines operator float().
+    4. Global or member operators for stringstream when converting from or to std::string (or FROM const char*)
+    5. Function that simply displays "Could not convert value" with information obtained from typeid().
+
+    A note: There has to be an exact type match (or according to the rules of template spec.) except for 3.
+
+    There are obviously a lot of ways to specifiy a user defined conversion. What should I use?
+    When using any non-template function based conversion (implicit conversion, explicitConversion, << or >>)
+    then you should consider that this function has to be defined prior to including this file.
+    If you do not whish do do that, you will have to spcecialsize the ConverterExplicit template.
+    There is a not so obvious advantage of the other way (non-template): You could declare each conversion function
+    in the Prereqs file of the corresponding library. Then you can use the conversion everywhere.
+    This is not possible with template specialisations even when defining them in this file (You would create
+    a circular dependency when using a class from Core for instance, because complete template specialisations
+    get compiled anyway (there is no template parameter)).
+*/
+
+// Put everything in a namespace to avoid unnecessary exposure
+// Note that the textual order of the functions is in reverse.
 namespace conversion
 {
@@ -220 +243 @@
     struct StringStreamPossible { };
 
-    // No Conversion possible, default template
+
+    ///////////////////
+    // No Conversion //
+    ///////////////////
+
+    // Default template, no Conversion possible
     template <class ToType, class FromType, int Dummy>
-    struct Converter
+    struct ConverterSS
     {
         static bool convert(ToType* output, FromType input)
         {
-            // Do not allow impossible conversions
-            //(*output) = input; // this WILL trigger a compiler error
-            //BOOST_STATIC_ASSERT(sizeof(ToType) == 0); // just to be sure..
+            COUT(2) << "Could not convert value of type " << typeid(FromType).name()
+                    << " to type " << typeid(ToType).name() << std::endl;
             return false;
         }
     };
-}
-
-
-///////////////////////
-//Explicit Conversion//
-///////////////////////
-
-namespace conversion
-{
-    // We can cast explicitely via function overloading, this overwrites any other possible cast
-    template <class ToType, class FromType>
-    inline bool convert(ToType* output, const FromType& input, ExplicitPossible<true>)
-    {
-        // This function can by anywhere globally!
-        //int a = TemplateDebugger<1,2>::debug(1,1);
-        //conversionTests::ExplicitConversion<FromType, ToType, 4>::test();
-        //BOOST_STATIC_ASSERT(0);
-        return explicitConversion(output, input);
-    }
-
-    // No function explict conversion, try implicit cast
-    template <class ToType, class FromType>
-    inline bool convert(ToType* output, const FromType& input, ExplicitPossible<false>)
-    {
-        return convert(output, input, ImplicitPossible<ImplicitConversion<FromType, ToType>::exists>());
-        //return ConverterSpecialised<ToType, FromType>::convert(output, input);
-    }
-}
-
-// template that is used when no explicit template specialisation is available
-template <class ToType, class FromType>
-struct ConverterSpecialised
-{
-    static bool convert(ToType* output, const FromType& input)
-    {
-        // check for explicit conversion via function overloading
-        return conversion::convert(output, input,
-            conversion::ExplicitPossible<ExplicitConversion<FromType, ToType>::exists>());
-    }
-};
-
-namespace conversion
-{
-    /////////////////
-    //Implicit Cast//
-    /////////////////
+
+
+    ///////////////////
+    // OStringStream //
+    ///////////////////
+
+    // Conversion via ostringstream
+    template <class FromType>
+    inline bool convertOStringStream(std::string* output, const FromType& input)
+    {
+        std::ostringstream oss;
+        if (oss << input)
+        {
+            (*output) = oss.str();
+            return true;
+        }
+        else
+            return false;
+    }
+
+    // template that evaluates whether OStringStream is possible for conversions to std::string
+    template <class FromType, int Dummy>
+    struct ConverterSS<std::string, FromType, Dummy>
+    {
+        // probe for '<<' stringstream operator
+        static bool convert(std::string* output, const FromType& input)
+        {
+            const bool probe = OStringStreamOperator<FromType>::exists;
+            return convert(output, input, StringStreamPossible<probe>());
+        }
+        // Conversion with ostringstream possible
+        static bool convert(std::string* output, const FromType& input, StringStreamPossible<true>)
+        {
+            return convertOStringStream(output, input);
+        }
+        // Conversion with ostringstream not possible
+        static bool convert(std::string* output, const FromType& input, StringStreamPossible<false>)
+        {
+            COUT(2) << "Could not convert value of type " << typeid(FromType).name()
+                    << " to std::string" << std::endl;
+            return false;
+        }
+    };
+
+
+    ///////////////////
+    // IStringStream //
+    ///////////////////
+
+    // conversion from std::string via istringstream
+    template <class ToType>
+    inline bool convertIStringStream(ToType* output, const std::string& input)
+    {
+        std::istringstream iss(input);
+        if (iss >> (*output))
+        {
+            return true;
+        }
+        else
+            return false;
+    }
+
+    // template that evaluates whether IStringStream is possible for conversions from std::string
+    template <class ToType, int Dummy>
+    struct ConverterSS<ToType, std::string, Dummy>
+    {
+        // probe for '>>' stringstream operator
+        static bool convert(ToType* output, const std::string& input)
+        {
+            const bool probe = IStringStreamOperator<ToType>::exists;
+            return convert(output, input, StringStreamPossible<probe>());
+        }
+        // Conversion with istringstream possible
+        static bool convert(ToType* output, const std::string& input, StringStreamPossible<true>)
+        {
+            return convertIStringStream(output, input);
+        }
+        // Conversion with istringstream not possible
+        static bool convert(ToType* output, const std::string& input, StringStreamPossible<false>)
+        {
+            COUT(2) << "Could not convert std::string value to type " << typeid(ToType).name() << std::endl;
+            return false;
+        }
+    };
+
+
+    ///////////////////
+    // Implicit Cast //
+    ///////////////////
 
     // We can cast implicitely
@@ -287 +357 @@
     }
 
-    // No implicit cast, leave it up to << and >>
+    // No implicit cast, leave it up to << and >> via template spcialisation
     template <class ToType, class FromType>
     inline bool convert(ToType* output, const FromType& input, ImplicitPossible<false>)
     {
-        return Converter<ToType, FromType, 0>::convert(output, input);
-    }
-
-
-    /////////////////
-    //OStringStream//
-    /////////////////
-
-    // Conversion via ostringstream
-    template <class FromType>
-    bool convertOStringStream(std::string* output, const FromType& input)
-    {
-        std::ostringstream oss;
-        if (oss << input)
-        {
-            (*output) = oss.str();
-            return true;
-        }
-        else
-            return false;
-    }
-
-    // template that evaluates whether OStringStream is possible
-    template <class FromType, int Dummy>
-    struct Converter<std::string, FromType, Dummy>
-    {
-        // convert to std::string, probe for '<<' stringstream operator
-        static bool convert(std::string* output, const FromType& input)
-        {
-            return convert(output, input, StringStreamPossible<OStringStreamOperator<FromType>::exists>());
-            //conversion::OStringStreamOperator<FromType>::test();
-        }
-
-        // Conversion with ostringstream possible
-        static bool convert(std::string* output, const FromType& input, StringStreamPossible<true>)
-        {
-            return convertOStringStream(output, input);
-        }
-
-        // Conversion with ostringstream not possible
-        static bool convert(std::string* output, const FromType& input, StringStreamPossible<false>)
-        {
-            // Do not allow impossible conversions
-            //(*output) = input; // this WILL trigger a compiler error
-            //BOOST_STATIC_ASSERT(sizeof(ToType) == 0); // just to be sure..
-            return false;
-        }
-    };
-
-
-    /////////////////
-    //IStringStream//
-    /////////////////
-
-    // conversion from std::string via istringstream
-    template <class ToType>
-    bool convertIStringStream(ToType* output, const std::string& input)
-    {
-        std::istringstream iss(input);
-        if (iss >> (*output))
-        {
-            return true;
-        }
-        else
-            return false;
-    }
-
-    // template that evaluates whether IStringStream is possible
-    template <class ToType, int Dummy>
-    struct Converter<ToType, std::string, Dummy>
-    {
-        // convert from std::string, probe for '>>' stringstream operator
-        static bool convert(ToType* output, const std::string& input)
-        {
-            return convert(output, input, StringStreamPossible<IStringStreamOperator<ToType>::exists>());
-        }
-
-        // Conversion with istringstream possible
-        static bool convert(ToType* output, const std::string& input, StringStreamPossible<true>)
-        {
-            return convertIStringStream(output, input);
-        }
-
-        // Conversion with istringstream not possible
-        static bool convert(ToType* output, const std::string& input, StringStreamPossible<false>)
-        {
-            // Do not allow impossible conversions
-            //(*output) = input; // this WILL trigger a compiler error
-            //BOOST_STATIC_ASSERT(sizeof(ToType) == 0); // just to be sure..
-            return false;
-        }
-    };
-
-
-    ///////////////
-    //const char*//
-    ///////////////
-
-    // delegate conversion from const char* via string
-    template <class ToType, int Dummy>
-    struct Converter<ToType, const char*, Dummy>
-    {
-        // convert from const char* via std::string
-        static bool convert(ToType* output, const char* input)
-        { return Converter<ToType, std::string, Dummy>::convert(output, input); }
-    };
-}
-
-
-////////////////////
-//Public Functions//
-////////////////////
+        return ConverterSS<ToType, FromType, 0>::convert(output, input);
+    }
+
+
+    /////////////////////////
+    // Explicit Conversion //
+    /////////////////////////
+
+    // We can convert explicitely via function overloading
+    template <class ToType, class FromType>
+    inline bool convert(ToType* output, const FromType& input, ExplicitPossible<true>)
+    {
+        // This function can by anywhere globally!
+        return explicitConversion(output, input);
+    }
+
+    // No explict conversion via explicitConversion(), try implicit cast
+    template <class ToType, class FromType>
+    inline bool convert(ToType* output, const FromType& input, ExplicitPossible<false>)
+    {
+        const bool probe = ImplicitConversion<FromType, ToType>::exists;
+        return convert(output, input, ImplicitPossible<probe>());
+    }
+
+    // template that is used when no explicit template specialisation is available
+    // try explicitConversion() function next.
+    template <class ToType, class FromType>
+    struct ConverterExplicit
+    {
+        static bool convert(ToType* output, const FromType& input)
+        {
+            // check for explicit conversion via function overloading
+            const bool probe = ExplicitConversion<FromType, ToType>::exists;
+            // why conversion:: ? --> below is a 'using' directive, so this template usually
+            // gets instantiated in global namespace
+            return conversion::convert(output, input, ExplicitPossible<probe>());
+        }
+    };
+}
+
+
+//////////////////////
+// Public Functions //
+//////////////////////
+
+// We usually don't have a namespace in util/ but it would still be desirable to lock
+// everything internal away in namespace conversion.
+using conversion::ConverterExplicit;
 
 /**
@@ -408 +414 @@
     Converts any value to any other as long as there exits a conversion.
     Otherwise, the conversion will generate a runtime warning.
+    For information about the different conversion methods (user defined too), see the section
+    'Actual conversion sequence' in this file above.
 */
 template <class ToType, class FromType>
 inline bool convertValue(ToType* output, const FromType& input)
 {
-    // check whether we can convert one type to the other explicitely via function overloading
-    //conversionTests::ExplicitConversion<FromType, ToType, 4>::test();
-    return ConverterSpecialised<ToType, FromType>::convert(output, input);
-    //return conversion::convert(output, input,
-    //    conversion::ExplicitPossible<ExplicitConversion<FromType, ToType>::exists>());
-}
-
-// Helper function: Calls convertValue with and without default value and returns true if the conversion was successful
+    // check whether we can convert one type to the other explicitely via explicit template specialisations
+    return ConverterExplicit<ToType, FromType>::convert(output, input);
+}
+
+// For compatibility reasons. The same, but with capital ConvertValue
 template<class FromType, class ToType>
-static bool ConvertValue(ToType* output, const FromType& input)
+inline bool ConvertValue(ToType* output, const FromType& input)
 {
     return convertValue(output, input);
 }
+
+// Calls convertValue and returns true if the conversion was successful.
+// Otherwise the fallback is used.
 template<class FromType, class ToType>
-static bool ConvertValue(ToType* output, const FromType& input, const ToType& fallback)
+inline bool ConvertValue(ToType* output, const FromType& input, const ToType& fallback)
 {
     if (convertValue(output, input))
@@ -435 +443 @@
 }
 
-// Helper function: Calls convertValue with and without default value and returns the converted value
+// Directly returns the converted value, even if the conversion was not successful.
 template<class FromType, class ToType>
-static ToType getConvertedValue(const FromType& input)
-{
-    ToType output = ToType();
+inline ToType getConvertedValue(const FromType& input)
+{
+    ToType output;
     ConvertValue(&output, input);
     return output;
 }
+
+// Directly returns the converted value, but uses the fallback on failure.
 template<class FromType, class ToType>
-static ToType getConvertedValue(const FromType& input, const ToType& fallback)
+inline ToType getConvertedValue(const FromType& input, const ToType& fallback)
 {
     ToType output = fallback;
@@ -451 +461 @@
 }
 
+// Like getConvertedValue, but the template argument order is in reverse.
+// That means you can call it exactly like static_cast<ToType>(fromTypeValue).
+template<class ToType, class FromType>
+inline ToType conversion_cast(const FromType& input)
+{
+    ToType output;
+    ConvertValue(&output, input);
+    return output;
+}
+
+// Like conversion_cast above, but uses a fallback on failure.
+template<class ToType, class FromType>
+inline ToType conversion_cast(const FromType& input, const ToType& fallback)
+{
+    ToType output = fallback;
+    ConvertValue(&output, input, fallback);
+    return output;
+}
+
+
+///////////////////////////////////////
+// Explicit Template Specialisations //
+///////////////////////////////////////
+
+// delegate conversion from const char* via std::string
+template <class ToType>
+struct ConverterExplicit<ToType, const char*>
+{
+    // convert from const char* via std::string
+    static bool convert(ToType* output, const char* input)
+    {
+        return conversion::ConverterSS<ToType, std::string, 0>::convert(output, input);
+    }
+};
+
+// These conversions would exhibit ambiguous << or >> operators when using stringstream
+template <> struct ConverterExplicit<std::string, char>
+{
+    static bool convert(std::string* output, const char input)
+    {
+        *output = std::string(input, 1);
+        return true;
+    }
+};
+template <> struct ConverterExplicit<std::string, unsigned char>
+{
+    static bool convert(std::string* output, const unsigned char input)
+    {
+        *output = std::string(input, 1);
+        return true;
+    }
+};
+template <> struct ConverterExplicit<char, std::string>
+{
+    static bool convert(char* output, const std::string input)
+    {
+        if (input != "")
+            *output = input[0];
+        else
+            *output = '\0';
+        return true;
+    }
+};
+template <> struct ConverterExplicit<unsigned char, std::string>
+{
+    static bool convert(unsigned char* output, const std::string input)
+    {
+        if (input != "")
+            *output = input[0];
+        else
+            *output = '\0';
+        return true;
+    }
+};
+
 #endif /* _Convert_H__ */