Enum as array size

[bvdberg]

(initiated by Chqrlie's idea)

Allow enum type as array size definer, like:
u8[Kind] kinds;

Advantages: it's very clear that the array size is linked to the enum. No hassle with gaps/elemsof/enum_max/etc

Restrictions for discussion:

• the enum-type used must start at 0 and be continuous (no gaps)
• when indexing, the index type must be that Enum. kinds[10] -> error
• dont allow u8[2*Kind] etc, only [Kind]
• multi-dimensional arrays (possibly with same/different enum types) are allowed

[chqrlie]

We should still be able to iterate over these arrays by indexing via a variable. If this variable is defined as a u32, this would be a constraint violation, so the iteration variable must either be cast when used as an index or have the appropriate type, which begs another question: how do we express this iteration?

We can write for (Kind k = Kind.min; k <= Kind.max; k++) but I don't really like this because it would fail if KInd is an enumeration that completely covers the set of values of its implementation type (eg: u8 for a bytecode interpreter).

For this reason, I think kinds[10] should be allowed but generate an error if 10 is not a valid Kind enum value, and kinds[i] should be allowed too but have undefined behavior if the value of i is not in the set of defined Kind enum values.

[bvdberg]

implemented