Re: Ada2012 : Expression functions and extended return statements

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Adam Beneschan <adam@irvine.com> writes:

> On Jan 6, 8:33�am, Adam Beneschan <a...@irvine.com> wrote:
>> On Jan 6, 12:45�am, Martin <mar...@thedowies.com> wrote:
>>
>> > Also, on the topic of extended return statements...
>>
>> > What's the rational for having to explicitly repeat the return type?
>> > Seems rather redundant to my eyes. I wouldn't have minded:
>>
>> > function Bar return Some_Type is
>> > begin
>> > � �return Result : <> do
>> > � � � -- something to initialise 'Result'
>> > � �end return;
>> > end Bar;
>>
>> > or even
>>
>> > function Bar return Some_Type is
>> > begin
>> > � �return Result do
>> > � � � -- something to initialise 'Result'
>> > � �end return;
>> > end Bar;
>>
>> > In this case, 'Result' can't be anything other than of type
>> > 'Some_Type' can it?
>>
>> Yes, it can. �If Some_Type is a class-wide type, Result's type must be
>> a specific type. �If Some_Type is, say, an unconstrained array type,
>> Result's type must be a constrained subtype.
>
> Oops, I goofed.  Result's type doesn't *have* to be a specific,
> constrained subtype, if there is an initial value (which could be a
> function call, say); the specific type and subtype are then determined
> from the value.  If there is no initial value, however, then Result's
> type does have to be constrained.

Well, the examples above don't have an initial value, so I took
your "must be constrained" comment to mean "for this example,
because there's no initial value".

Anyway, the rule is the same as for an object_declaration -- if there's
no initial value, the subtype has to be definite.

- Bob