Adjust primitive not called on defaulted nonlimited controlled parameter, bug or feature ?

[David SAUVAGE]

In the code extract below [2] Adjust primitive is not called on defaulted nonlimited controlled parameter Set.
A reproducer is available on gitlab [1]

Seems like a bug, any feedbacks ?

[1]
reproducer
https://gitlab.com/adalabs/reproducers/-/tree/main/adjust-not-called-on-defaulted-nonlimited-controlled-parameter

[2]
1 with Ada.Exceptions,
2 Ada.Text_IO;
3
4 with GNAT.OS_Lib;
5
6 procedure Reproducer.Main is
7
8 --
9 -- snippet of reproducer.ads
10 -- ...
11 -- type Translate_Set is private;
12 -- Null_Set : constant Translate_Set;
13 -- private
14 -- type Translate_Set is new Ada.Finalization.Controlled with record
15 -- Ref_Count : Integer_Access;
16 -- Set : Boolean_Access;
17 -- end record;
18 -- Null_Set : constant Translate_Set := (Ada.Finalization.Controlled with null, null);
19 -- ...
20 --
21
22 procedure Process (Set : Translate_Set := Null_Set)
23 is
24 Content : constant String := Parse (Filename => "Process",
25 Translations => Set);
26 begin
27 Ada.Text_IO.Put_Line (Content);
28 end Process;
29 begin
30 Process;
31 -- Ok, Initialize (Set) is not called because default value Null_Set is specified to Set (7.6 10/2).
32 -- However Adjust (Set) is not called (7.6 17.8/3).
33 -- Is it a feature or a bug ?
34
35 exception
36 when E : others =>
37 Ada.Text_IO.Put_Line ("(FF) Adjust was not called on the nonlimited controlled object Set, when parameter defaulted to Null_Set");
38 Ada.Text_IO.Put_Line ("(FF) " & Ada.Exceptions.Exception_Information (E));
39 GNAT.OS_Lib.OS_Exit (255);
40 end Reproducer.Main;

[Jere]

Since Translate_Set is a "by-reference type" (see section 6.2 of the RM), there isn't an
assignment actually made is my guess. The default parameter notation looks like assignment, but
I would hazard a guess that it doesn't mean an actual assignment is required.

[Jeffrey R.Carter]

On 2022-08-17 22:11, David SAUVAGE wrote:
> In the code extract below [2] Adjust primitive is not called on defaulted nonlimited controlled parameter Set.
> A reproducer is available on gitlab [1]
>
> Seems like a bug, any feedbacks ?

Adjust is called on assignment. Your code does no assignments.

--
Jeff Carter
"The time has come to act, and act fast. I'm leaving."
Blazing Saddles
36

[Randy Brukardt]

"Jeffrey R.Carter" <spam.jrc...@spam.acm.org.not> wrote in message
news:tdk03o$kljt$1...@dont-email.me...

> On 2022-08-17 22:11, David SAUVAGE wrote:
>> In the code extract below [2] Adjust primitive is not called on defaulted
>> nonlimited controlled parameter Set.
>> A reproducer is available on gitlab [1]
>>
>> Seems like a bug, any feedbacks ?
>
> Adjust is called on assignment. Your code does no assignments.

Right. A default parameter that is an object (as in this case) is simply
passed to the subprogram, so there is no assignment when that happens, and
thus no Adjust. If the default had been an aggregate or some more complex
expression, then there would have been a new, temporary object. But new
objects can be built-in-place, and if so, there is no assignment and no
adjust (of the whole object, individual components are assigned).
Build-in-place is required in some contexts, and since compilers have to
implement it for those contexts, and it is cheaper in most contexts, it is
likely to be used on almost all new objects (especially temporaries).

It is tricky to determine precisely when non-limited controlled objects are
Adjusted; the main rule of thumb is that any object that is Initialized or
Adjusted will be Finalized, but one should not count on any particular
number or order of Adjusts or Initializes.

Anyway, the point is that one should never expect an Adjust to be associated
with parameter passing; it could be in a few cases, but even then it could
be omitted with different compiler settings (or a different compiler).

Randy.

[David SAUVAGE]

> Adjust is called on assignment. Your code does no assignments.
> Right. A default parameter that is an object (as in this case) is simply
> passed to the subprogram, so there is no assignment when that happens, and
> thus no Adjust.

Thanks Jere, Jeffrey and Randy.

reproducer updated accordingly
https://gitlab.com/adalabs/reproducers/-/raw/main/adjust-not-called-on-defaulted-nonlimited-controlled-parameter/sources/reproducer-main.adb