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Newsgroups: comp.lang.ada
Date: Sat, 18 Jan 2020 10:02:31 -0800 (PST)
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Subject: Re: Calling a record type's methods (functions or procedure) when
 record is in an array
From: Mace Ayres <maceayres0@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:57877
Date: 2020-01-18T10:02:31-08:00
List-Id: <comp.lang.ada>

Thank you. I see, we can pass the record (type) thing as a parameter, along=
 with any other parameters (like value) and then interact with the record =
=E2=80=98thing=E2=80=99  in sub programs.=20

Since my objects (type of Thing) are only instantiated as elements in my ar=
ray, thing_array, I can only/ would I address them like this ?

looping.. i
 looping  j
   set_attribute(my_thing_array(i,j).value, 6);
  ...
end loop;
end loop;

In this way I only access (not ACCESS type) my thing via set_attribute proc=
edure and not with...  thing.value :=3D 5, which is the direct access we wa=
nt to avoid.=20

And with type thing being private, its attributes are only accessible via s=
ub programs in package Mace.

In your code below with my mark up =E2=80=9C * ?=E2=80=9D,  are the sub pro=
grams private in any way since they are below  Type Thing is private, or th=
e privacy is applied to Thing?

That is, what is the full scope of privacy in declaring type thing as priva=
te, to type thing only,  or the sub programs too. Or is this a confused que=
stion anyway?


? this code does indeed access the value fields directly!

-- I have to add the private part too, to hide the inners of type
a_trunk.

You're looking for an accessor (though accessors aren't always a good
idea; there might be checks needed, attributes may be related so you
need to deal with more than one at the same time, eg coordinates):

 package Mace is
    type Thing is private;
 * ?    procedure Set_Attribute (Into : in out Thing; Value : Integer);
 * ?   function Get_Attribute (From : Thing) return Integer;
 private
    type Thing is record
       Attribute : Integer;
    end record;
 end Mace;

 package body Mace is
    procedure Set_Attribute (Into : in out Thing; Value : Integer) is
    begin
       Into.Attribute :=3D Value;
    end Set_Attribute;
    function Get_Attribute (From : Thing) return Integer
    is (From.Attribute);
 end Mace;