Re: What would you like in Ada202X?

["Randy Brukardt" <randy@rrsoftware.com>]

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:a0rsroFp8lU1@mid.individual.net...
(Commenting only on the side-track)

...
> This is a side track, but I don't see any compelling reason (except 
> compatibility) to define a standard default representation for enumeration 
> types. There is no standard representation for Booleans, integer types, 
> floats, records; why should enumeration types have one? (Is it a remnant 
> of a C-style identification of enumerations with integers?)
>
> Decades ago I liked to specify my own enumeration representations, but I 
> would think three times before doing it today. It is only useful for 
> unchecked conversions and I/O. If you use it for input, you have to mess 
> about with 'Valid or exceptions.

'Valid *and* exceptions. You can never assume that Program_Error is not 
raised; using an invalid value is a bounded error and the compiler is 
definitely allowed to raise Program_Error if the error is detected. (And 
Janus/Ada does detect it; as I previously noted, it uses the Position number 
for all operations, and if there is no Position number for a value, we have 
to do something, and the language says that is "raise Program_Error;")

> For output, there are always other important considerations like memory 
> access width and byte ordering.

I wasn't arguing that this capability is important, only that Ada has it and 
both the language design and the implementation have to take the possibility 
into account. We're surely not removing this capability!

It's the same with the default representation for enumeration values. 
Probably 98% of Ada programs don't care at all about the representation, but 
even if only 0.1% do, changing it would break too many programs to consider 
it. (And the Unchecked_Conversion usage is not that unusual.)

A new kind of enumeration type could have different rules, but that's 
confusing (since sometimes you can depend on the representation and sometime 
you can't).

                                 Randy.