Re: Bases 1.52

["Robert I. Eachus" <rieachus@attbi.com>]

Nick Roberts wrote:
> "Robert I. Eachus" <rieachus@attbi.com> wrote in message
> news:3F64B1B3.2070305@attbi.com...
> 
> 
>>But like unbounded string types, or a discriminated record
>>type without a default value for the discriminant, you must
>>provide an initial value
> 
> 
> An initial value is not required for an object of type
> Ada.Strings.Unbounded.Unbounded_String. It is initialised by default to an
> empty string [RM95 A.4.5.(73)]. I guess you meant "... like objects declared
> as being of an unconstrained subtype with no constraint, such as 'String',
> or of a discriminated record subtype which does not have default expressions
> for the discriminants and with no constraint, ...".

That is why I said unbounded string types--all lower case--not type 
Unbounded_String.  But I did make a mistake, I really meant to write 
unbounded array types, which is a lot clearer.


> Do you mean other than the term "indefinite"? [RM95 3.3(23), 3.7(26)]

Yes.  But it is really hard to express what I meant.  There are types 
whose subtype is indefinite, where you can either add a constraint when 
declaring an object, or provide an initial value.  But there are also 
indefinite types where you cannot provide a constraint, and must provide 
an initial value.  These are currently "types with unknown 
discriminants" all types with unknown discriminants are indefinite, but 
not all indefinite subtypes are types with unknown discriminants.

I think in one ARG discussion we called these types "really indefinite 
types" and in another discussion "initial value only types" but neither 
of those names is much shorter than "types with unknown discriminants." 
  (Notice that classwide types are not really types with unknown 
discriminants, but 3.3(29) defines them to be.)

This may seem to be much ado about nothing, but these types are those 
that cannot be subcomponents, so it is a pretty important group.

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