On 11/07/2019 15:46, J. Gareth Moreton wrote: > Outside of typecasting, there isn't a reliable way to check if an enum > contains a valid value
Typecasting is not a reliable way. There is no and cannot be a reliable way, period. > For my personal point of view, I would like these operators to be the > exception to the rule of the compiler assuming an enum always contains a > valid value, This is the crux of the whole issue. Type systems do not and cannot work this way. At its heart, this discussion is not about compiler assumptions, optimisations, exploiting undefined behaviour etc. It's that if a language has a type system, then by definition all reasoning over programs written in this language must follow the rules of this type system. A fundamental part of this is that a variable of type X can store all values that are valid for type X. Not more, and not less. This is true for FPC, Delphi, C, C++, C#, Java, ADA any every other programming language in existence that has a type system. Otherwise you do not have a type system, but at most some ad hoc behaviours that vaguely resemble a type system. You can never deviate from this, or you end up with an unmaintainable and unpredictable mess (regardless of how well you know the basic rules of the language, and not just when you are used to type system with different rules). In Delphi's type system (and in C, C++, and C#), the valid values for an enum are always all values that fit within its storage size, and that storage size is fixed. In FPC's type system (and in Ada and Java), the valid values for an an enum are only the values between the lowest and the highest declared enum element (in Java it's even more strict, in that when you have "enums with holes", the holes are also invalid), regardless of the storage size. Moreover, this storage size can vary depending on whether or not the item is in bitpacked storage. That definition of enums is also what allows us to bitpack these types in the first place, since otherwise we would not be able to store all valid values for enums in their bitpacked versions. Jonas _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
