Hi I'm trying to have enum outside of class but inside namespace AND have them have different definition depending on some condition. How can I achieve this? (C++)
For example something like this
namespace fruit {
if (season) {
enum eAvailfruit
{
apple,
banana,
cNumFruit
};
} else {
enum eAvailfruit
{
watermelon,
grape,
peach,
cNumFruit
};
}
}
Is there a way ??
One approach would be to use the preprocessor:
#ifdef SUMMER
enum Fruit {
// ....
};
#else
enum Fruit {
// ...
};
#endif
and then pass a compile-time constant in whatever way your compiler normally prefers it, for example the -D flag in gcc.
Or, on the other hand, don't, because it's a terrible idea. One slightly better solution might be the following:
enum Season {
Spring,
Summer,
Autumn,
Winter
};
template <Season S>
struct fruit; // undefined
template <>
struct fruit<Spring>
{
enum AvailableFruit {
Banana,
// etc
};
};
template <>
struct fruit<Summer>
{
enum AvailableFruit {
// etc
};
};
// etc, specialisations for Autumn and Winter
These structs are then fairly similarly to C++11 scoped enums, in that you can refer to (for example) fruit<Spring>::Banana, but they're type safe as it's illegal to refer to just plain Banana, or even just plain AvailableFruit.
seasonis a compile-time constant, but not otherwise.season?bananathen what will happen whenseasonis false?