Re: Question about finalization of local object returned from the function

[Stephen Leake <stephen_leake@stephe-leake.org>]

On Wednesday, August 28, 2019 at 6:45:16 PM UTC-7, Brad Moore wrote:
> On Wednesday, August 28, 2019 at 4:36:38 PM UTC-6, darkestkhan wrote:
> > Given a function returning controlled type:
> > 
> > function Bar return T is
> >   Foo : T;
> > begin
> >   ...
> >   return Foo;
> > end Bar;
> > 
> > would Foo be finalized upon end of the function?
> > 
> 
> Yes Foo is finalized upon end of the function, but not before copying the
> object to a temporary result object which is returned to the caller. The temporary is finalized also after being assigned to the result object.
> In other words, the expected result is returned to the caller, and the Foo object on the stack is also properly finalized.
> 

However, the compiler is free to optimize away any of these steps, as long as the net effect is preserved.

To expand on Brad's comment about the extended return statement, consider:

function Bar return T is
begin
   return Foo : T do
      ...
   end return;
end Bar;

then 'Foo' is actually the object that the client has declared/allocated. For example:

declare
   A : T := Bar;
begin
...

"Foo" is actually "A", so no temporary objects are required. 

I don't think Limited_Controlled is required for this to happen; ARM 6.5 (24/3) mentions "built in place", but not Limited_Controlled. Also ARM 7.6 (17.1/3) gives the conditions where "built in place" is required.

-- Stephe