Re: "Ada Gems": Constructor functions

["Jeffrey R. Carter" <spam.jrcarter.not@acm.nospam.org>]

Tomek Wa�kuski wrote:
> 
> with Ada.Strings.Unbounded;
> use Ada.Strings.Unbounded;
> 
> package T is
>     type Object (<>) is tagged limited private;
> 
>    function Create_Object (Name : in String) return Object;
>    function Construct return Object;
>    function Name (This : in Object) return String;
> 
>    type Object is tagged limited
>       record
>          Name : Unbounded_String;
>       end record;
> end T;

T has a private type (Object) but no private part.

> package body T is
>    function Create_Object (Name : in String) return Object is
>       return (Name => To_Unbounded_String (Name));
>    end Create_Object;
> 
>    function Construct return Object is
>       return Create_Object (Name => "Object without a name!");
>    end Construct;
> 
>    function Name (This : in Object) return String is
>    begin
>       return To_String (This.Name);
>    end Name;
> 
>    type Object is tagged limited
>       record
>          Name : Unbounded_String;
>       end record;
> end T;

Type Object is repeated here.

> with T;
> 
> procedure Test_T is
>    Some_Object : constant T.Object := Construct;
> begin
>    null;
> end Test_T;

Construct is not directly visible here.

> Is it REALLY a compiler bug? Or am I only dumb? :) Maybe I'm doing
> something, somewhere wrong?

It's really a compiler error. A compiler should be able to handle the 
errors in your code without crashing.

FWIW, I got this with another version:

gnatmake -O2 -gnaton -fstack-check test_t.adb
gcc -c -O2 -gnaton -fstack-check test_t.adb
test_t.adb:4:39: "Construct" is not visible
test_t.adb:4:39: non-visible declaration at t.ads:8
t.ads:11:04: declaration of full view must appear in private part
gnatmake: "test_t.adb" compilation error

-- 
Jeff Carter
"Death awaits you all, with nasty, big, pointy teeth!"
Monty Python & the Holy Grail
20