Re: Ada2012 : Expression functions and extended return statements

[Martin <martin@thedowies.com>]

On Jan 6, 11:23 am, "Peter C. Chapin" <PCha...@vtc.vsc.edu> wrote:
> On 2012-01-06 05:02, Martin wrote:
>
> > I still think it would be nice to have a short-hand e.g. 'return
> > Result :<>  do'. If anything it would then draw the eye to the more
> > interesting case when the 2 are different.
>
> You need to repeat the type for ordinary returns as well.
>
> function F return Integer is
>    Result : Integer;  -- Duplication of return type here.
> begin
>    Result := 1;
>    return Result;
> end F;
>
> To be consistent it seems like you'd need to be able to use '<>'
> throughout the body of the function.
>
> function F return Integer is
>    Result : <>;  -- Shorthand for function's return type.
> begin
>    Result := 1;
>    return Result;
> end F;
>
> Considering Ada's tendency to require one to repeat information in
> earlier declarations, this seems a bit unAda-like to me. Also this would
> allow '<>' to show up in a lot of strange looking places such as type
> conversions and type qualifications.
>
> Peter

The difference is that the declaration of 'Return' in the extended
return is that the compiler 'knows' that this is the declaration of
something that's going to be returned - it can't know that in the
ordinary return case. Well, at least not when it first parses the
declaration, not without just assuming it is...and that might be
messy...

It would certainly be a departure from current Ada - adding a little
bit of "Type Inferencing" to the language. But I'm not adverse to
that...so long as the inferencing is safe. I like SML/NJ :-)

It's not that big a leap, at least not in my head, as "<>" is already
used to mean "default" (i.e. infer what I mean from what's visible)
and this would simply be "use the default return type, i.e. the one
that's in the the function declaration".

-- Martin