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Newsgroups: comp.lang.ada
Date: Wed, 6 Nov 2013 11:54:02 -0800 (PST)
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Subject: Re: Question about asynchronous calls
From: Shark8 <onewingedshark@gmail.com>
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Xref: number.nntp.dca.giganews.com comp.lang.ada:183786
Date: 2013-11-06T11:54:02-08:00
List-Id: <comp.lang.ada>

On Wednesday, November 6, 2013 4:05:44 AM UTC-7, mockturtle wrote:
> Dear all,
>=20
> I am scheduled to give an introductory talk (45 min) about Ada at the nex=
t "Open Source Day" here in Udine.  I was thinking about giving an overview=
 of the language, emphasizing those parts that are unique (or almost unique=
) to Ada, with the objective of making people curious.=20

While it doesn't seem like a big thing: subtypes.
It's nice not to have to check results of some-function from obviously-inco=
rrect-but-technically-possible values like we have to in C/C++/PHP:

Ex: Some_Array'Length returns Natural, I don't have to check for -1 wheneve=
r I use it.

And that's from all the way back to Ada 83, with Ada 2012 we have subtype-p=
redicates and can say the following:

    -- Refactor to a parent-type for SSN or EID.
    -- Note SSN is 11 characters long, EIN is 10.
    Type ID_String is new String
      with Dynamic_Predicate =3D> ID_String'Length in 10|11;

    -- SSN format: ###-##-####
    Subtype Social_Security_Number is ID_String(1..11)
      with Dynamic_Predicate =3D>
	(for all Index in Social_Security_Number'Range =3D>
          (case Index is
           when 4|7 =3D> Social_Security_Number(Index) =3D '-',
           when others =3D> Social_Security_Number(Index) in '0'..'9'
          )
         );

    -- EIN format: ##-#######
    Subtype EIN is ID_String(1..10)
      with Dynamic_Predicate =3D>
	(for all Index in EIN'Range =3D>
          (case Index is
           when 3 =3D> EIN(Index) =3D '-',
           when others =3D> EIN(Index) in '0'..'9'
          )
         );

    -- A string guaranteed to be an SSN (###-##-####) or EIN (##-#######).
    Subtype Tax_ID is ID_String
      with Dynamic_Predicate =3D>
          (Tax_ID in Social_Security_Number) or
          (Tax_ID in EIN);

> Among other things, I am planning about saying something about the existe=
nce of Annex E for distributed systems. =20
>=20
> While reading section "E.4.1. Asynchronous Remote Calls" of our beloved R=
M, I got a doubt: as I understand the language does not define any specific=
 mechanism for getting the "return value" of an asynchronous call; if I wan=
t the result back I must implement the "back channel" by myself (e.g., a ca=
llback or a polling function of type "are we there yet?" [to be said with c=
hildish voice] :-).  Am I right?

Sorry, I haven't used asynchronous-calls.