static int number(String name)
    {
        if (name.length() != 1)
            return 0;

        switch (name.charAt(0))
        {
            case 'a':
                return ID_ENUM_VALUE;
            case 'x':
                return ID_ENUM;
            default:
                return 0;
        }
    }
Used when a field is declared as {@code Enum<?>} (with or with-out generics).

@author David Yu
@created Apr 25, 2012
protostuff-runtime/src/main/java/io/protostuff/runtime/PolymorphicEnumSchema.java