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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?= =?utf-8?Q?=29?=
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Newsgroups: comp.lang.ada
Subject: Re: Ada 2012: In-out parameters for functions
Date: Tue, 07 May 2013 05:59:49 +0200
Organization: Ada @ Home
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Date: 2013-05-07T05:59:49+02:00
List-Id: <comp.lang.ada>

Le Sun, 05 May 2013 12:24:50 +0200, Niklas Holsti  =

<niklas.holsti@tidorum.invalid> a =C3=A9crit:

> On 13-05-04 02:29 , Randy Brukardt wrote:
>
>> I agree that named notation should include the direction of the  =

>> parameter,
>> but again its way too late to fix. The best syntax would have been
>>      Proc (In_Param =3D> A, Out_Param <=3D B, In_Out_Param <=3D> C);
>> but unfortunately "<=3D" is used for less-than-or-equals and trying t=
o  =

>> use it
>> in this context would be ambiguous.
>>
>> So the best practical syntax would be:
>>      Proc (In_Param -> A, Out_Param <- B, In_Out_Param <-> C);
>
> How about reusing the mode keywords:
>
>    Proc (
>       In_Param  =3D> in A,
>       Out_Param =3D> out B,
>       In_Out_Param =3D> in out C);
>

As another option if you are not afraid about a lot of restrictions, the=
re  =

is one which won't make parameters modes visible, but which will surely =
 =

catch any erroneous assumptions on these, due to an assertion on the  =

effect of calling it, failing sooner or later:


     -- SPARK way to solve the issue
     -- and to make explicit what it do.

     procedure P
       (A :    out T;
        B : in out T;
        C : in     T);
     --# derives
     --#    A from B, C &
     --#    B from B, C ;


As a bonus, this could even catch far more errors than simply reminding =
 =

parameter modes :-P =E2=80=A6 but forget about generic packages [1], sub=
types [2]  =

and many other things.

[1]: library level generic sub=E2=80=91programs is OK, but this has the =
 =

implication a generic cannot defines types, constants, etc.
[2]: the last time I tried it, only type=E2=80=91new was allowed, not su=
re if it's  =

still the same now; may check later.

-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D [1]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [1]
[1]: Epigrams on Programming =E2=80=94 Alan J. =E2=80=94 P. Yale Univers=
ity