Re: Valid Attribute and Unchecked Conversion

[kst@thomsoft.com (Keith Thompson)]

In <Dyr7Dt.HqL@world.std.com> bobduff@world.std.com (Robert A Duff) writes:
[...]
> They shouldn't be, because, as you explained, they don't work.  Using
> sparse enums is asking for erroneousness.
[...]
> The whole feature causes an awful lot of complexity in compilers,
> given that it's not very useful.  Sigh.

Especially since it wouldn't have been difficult to make them useful.

The root of the problem, I think, is Ada 83's emphasis (not entirely
successful) on guaranteeing that representation clauses affect only
representation, not semantics.  In the case of enumeration types, this
was carried just a little too far, IMHO.

For example, the language could have defined two additional attributes,
analagous to 'Pos and 'Val, but operating on the internal representation
of an enumeration type.  If the argument is an invalid representation,
simply raise Constraint_Error.  GNAT provides half of this with its
'Enum_Rep attribute.

-- 
Keith Thompson (The_Other_Keith) kst@thomsoft.com <*>
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