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Date: Tue, 14 Apr 2020 02:42:10 -0700 (PDT)
In-Reply-To: <874ktofymo.fsf@samuel>
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Subject: SOLVED: Generic oddness
From: Per Jakobsen <pdj@knaldgas.dk>
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Xref: reader01.eternal-september.org comp.lang.ada:58356
Date: 2020-04-14T02:42:10-07:00
List-Id: <comp.lang.ada>

s=C3=B8ndag den 12. april 2020 kl. 18.38.11 UTC+2 skrev Ludovic Brenta:
>=20
> The part that I don't understand is why you can instantiate Gen but not
> Doubly_Linked_Lists with the same actual type as parameter; I think the
> instantiation of Doubly_Linked_Lists should freeze the type A_Intf just
> like package Workaround does.

I believe I've found the explanation:
A friend reminded me that our mutual friend Jacob Sparre Andersen actually =
reported this problem back in Sep 2017 (ticket: Q904-007) which was reporte=
d fixed in June 2019.

The problem is the equality function required for Doubly_Linked_List. If I =
add a similar function parameter to the Gen generic, it fails as well.

Apparently the implicitly declared equality operator for a type implementin=
g an Interface is treated as abstract until the type is frozen, which can b=
e done in several different ways.

Anyway it seems to be a problem that has been fixed in the recent compiler,=
 soon to be released in the Community Edition.

~Per