Question

This is the code snippet:

#include <boost/utility.hpp>
#include <boost/type_traits.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <boost/typeof/typeof.hpp>

enum ScriptVarType_t { SVT_BOOL, SVT_STRING, SVT_CUSTOM, SVT_CustomWeakRefToStatic };

struct ScriptVar_t {};
struct CustomVar {
    struct Ref {};
    struct WeakRef {};
};

template<typename T> struct GetType;

template<typename T> struct _GetTypeSimple {
    typedef T type;
    static type defaultValue() { return T(); }
    static const type& constRef(const type& v) { return v; }
};

template<> struct GetType<bool> : _GetTypeSimple<bool> { static const ScriptVarType_t value = SVT_BOOL; };
template<> struct GetType<std::string> : _GetTypeSimple<std::string> { static const ScriptVarType_t value = SVT_STRING; };
template<> struct GetType<CustomVar::Ref> {
    typedef CustomVar::Ref type;
    static const ScriptVarType_t value = SVT_CUSTOM;
    static type defaultValue() { return type(); }
    static const type& constRef(const type& v) { return v; }
};


template<typename T>
struct CustomVarWeakRefType {
    typedef CustomVar::WeakRef type;
    static const ScriptVarType_t value = SVT_CustomWeakRefToStatic;
    static CustomVar::Ref defaultValue() { return T().getRefCopy(); }
    static CustomVar::WeakRef constRef(const T& v) { return v.thisRef.obj; }
};

struct StringType : GetType<std::string> {};

template<typename T>
struct _SelectType {
    static CustomVarWeakRefType<T>* selectType(const CustomVar&) { return NULL; }

    static StringType* selectType(const char*) { return NULL; }
    static StringType* selectType(char[]) { return NULL; }

    typedef typename BOOST_TYPEOF(*selectType(*(T*)NULL)) type;
};

template<typename T> struct GetType : _SelectType<T>::type {};

template<typename T>
T _CastScriptVarConst(const ScriptVar_t& s, T*, typename boost::enable_if_c<(GetType<T>::value < SVT_CUSTOM), T>::type*) {
    return (T) s;
}

template<typename T>
T _CastScriptVarConst(const ScriptVar_t& s, T*, typename boost::enable_if_c<boost::is_base_of<CustomVar,T>::value, T>::type*) {
    return *s.as<T>();
}

Some of the errors:

3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(416): error C2059: Syntaxfehler: ')'
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(416): error C2143: Syntaxfehler: Es fehlt ',' vor ')'
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(416): error C2947: ">" wird erwartet, um template-argument-list abzubrechen. ">" wurde gefunden.
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(416): warning C4346: 'GetType<T>::value<T>::type': Abhängiger Name ist kein Typ
3>          Präfix mit 'typename' zum Angeben eines Typs
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(416): error C2059: Syntaxfehler: ')'
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(421): error C2059: Syntaxfehler: ','
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(421): warning C4346: 'boost::is_base_of<CustomVar,T>::value': Abhängiger Name ist kein Typ
3>          Präfix mit 'typename' zum Angeben eines Typs
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(421): error C2143: Syntaxfehler: Es fehlt ',' vor ')'
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(421): error C2143: Syntaxfehler: Es fehlt ';' vor '{'
3>c:\users\albert zeyer\programmierung\openlierox\include\CScriptableVars.h(423): error C2143: Syntaxfehler: Es fehlt ';' vor '}'

(Btw., any way to get these messages in English? I’m new to MSVC. E.g., it says: “>” is expected to cancel template-argument-list, but “>” was found.)

The error messages are mostly totaly stupid or wrong.

Why is that? I don’t even really see at what part MSVC is struggling.

How can I work around it?

Answer 1

Ok, found the problem. The less-comparison in enable_if_c<(GetType<T>::value < SVT_CUSTOM), T> confuses the compiler because it cannot really know that value is an integer.

I changed it to GetType<T>::value <= SVT_CUSTOM-1 and it all works fine.