From: Natasha Kerensikova <lithiumcat@instinctive.eu>
Subject: Loss of visibility of class-wide operation in prefix notation
Date: Sat, 5 Apr 2014 15:09:07 +0000 (UTC)
Date: 2014-04-05T15:09:07+00:00 [thread overview]
Message-ID: <slrnlk074k.i0l.lithiumcat@nat.rebma.instinctive.eu> (raw)
Hello,
I have been encountering some strange behavior of GNAT, and I wonder
whether it's a compiler bug or whether I'm doing something illegal.
Please consider the following code, it's a bit long but hopefully clear
enough:
package Root_Interface is
type T is interface;
procedure Process (Self : in out T; Result : out Boolean) is abstract;
procedure Process (Self : in out T'Class);
-- Call Process and discard Result
end Root_Interface;
package body Root_Interface is
procedure Process (Self : in out T'Class) is
Result : Boolean;
begin
Process (Self, Result);
end Process;
end Root_Interface;
package Root_Interface.Extension is
type T is interface and Root_Interface.T;
procedure Self_Check (Self : in out T) is abstract;
end Root_Interface.Extension;
with Root_Interface.Extension;
package Root_Interface.Half_Implementation is
type T is abstract new Extension.T with private;
not overriding procedure Subprocess (Self : in out T) is abstract;
overriding procedure Process (Self : in out T; Result : out Boolean);
overriding procedure Self_Check (Self : in out T);
type Example is new Extension.T with private;
private
type T is abstract new Extension.T with null record;
type Example is new T with record
Count : Natural := 0;
end record;
overriding procedure Subprocess (Self : in out Example);
end Root_Interface.Half_Implementation;
package body Root_Interface.Half_Implementation is
overriding procedure Process (Self : in out T; Result : out Boolean) is
begin
Subprocess (T'Class (Self));
Result := True;
end Process;
overriding procedure Self_Check (Self : in out T) is
begin
raise Program_Error;
end Self_Check;
overriding procedure Subprocess (Self : in out Example) is
begin
Self.Count := Self.Count + 1;
end Subprocess;
end Root_Interface.Half_Implementation;
package Root_Interface.Half_Implementation.Tests is
procedure Test_Suite;
end Root_Interface.Half_Implementation.Tests;
package body Root_Interface.Half_Implementation.Tests is
procedure Test_Suite is
Object : Example;
begin
Object.Process;
end Test_Suite;
end Root_Interface.Half_Implementation.Tests;
The basic idea is that I have a general root abstract type, used by most
clients of the library, with an optional extension. Then in a specific
of set of situations I can massively refactor the code, which leads to
the abstract "half-implementation", the other (mush smaller) half being
provided in concrete types by overriding the abstract primitive. In the
same package I also provide a basic concrete type, as an example to make
the code more self-documenting and to be used in the test suite.
The test suite itself is in a child package so that it can peek into the
implementation for whitebox tests.
So far everything is fine, and GNAT-AUX 4.9.0 compiles it happily.
But now I realize I need user-defined finalization in a concrete type
which inherits from Root_Interface.Half_Implementation.T, so I change it
to derive from Ada.Finalization.Controlled, without overriding anything:
with Ada.Finalization;
with Root_Interface.Extension;
package Root_Interface.Half_Implementation is
type T is abstract new Ada.Finalization.Controlled and Extension.T
with private;
not overriding procedure Subprocess (Self : in out T) is abstract;
overriding procedure Process (Self : in out T; Result : out Boolean);
overriding procedure Self_Check (Self : in out T);
type Example is new Extension.T with private;
private
type T is abstract new Ada.Finalization.Controlled and Extension.T
with null record;
type Example is new T with record
Count : Natural := 0;
end record;
overriding procedure Subprocess (Self : in out Example);
end Root_Interface.Half_Implementation;
And suddenly, GNAT rejects the test suite:
Compiling: root_interface-half_implementation-tests.adb
(source file time stamp: 2014-04-05 14:51:26)
6. Object.Process;
|
>>> missing argument for parameter "Result" in call to "Process"
ted) at root_interface-half_implementation.ads:15
However, when switching to traditional notation "Process (Object);"
everything is still fine. Moreover, when
Root_Interface.Half_Implementation.T implements Root_Interface.T rather
than the extension, everything still works fine.
Would you have any idea what I am doing wrong?
Thanks for your help,
Natasha
next reply other threads:[~2014-04-05 15:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-05 15:09 Natasha Kerensikova [this message]
2014-04-07 15:30 ` Loss of visibility of class-wide operation in prefix notation Adam Beneschan
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