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Date: 16 Apr 92 07:57:01 GMT
From: eru.mt.luth.se!lunic!sunic!sunic2!seunet!lin.foa.se!eriks@bloom-beacon.mi
t.edu  (Erik Svensson FOA2)
Subject: Re: associate functions to objects
Message-ID: <1992Apr16.075701.5312@lin.foa.se>
List-Id: <comp.lang.ada>

consp10@bingsunb.cc.binghamton.edu (Julian Insan Kamil) writes:

>I'm working on a project for a Software Engineering class, and we're using Ada
 to
>develop a simple database management application. My part is on building the u
ser
>interface for the app. One of the data type that we're using is called an
>EntryBoard which is supposed to manage a list of other objects like Fields,
>Buttons, Titles, etc. Each of those objects should be attached to a function t
hat
>will be called whenever that object is selected (sort of like callback
>functions). Now, how do you attach functions to objects? I consulted my Ada
>references and it seems that Ada doesn't allow passing functions as a paramete
r
>to a procedure (the way I did it in C++ to implement the same behavior). I nee
d
>hints and advice and examples on how to do this kind of things. Will anybody h
elp
>me with some light? 

If you're going to use generics you can send a procedure or a function as an
argument when you instantiate (sp?) the package. 

(this is from the top of my head, so there might be some errors)
generic
	type Type_1 is (<>);
	type Type_2 is private;
	with procedure Foo(a : in out Type_1); -- Your supplied procedure
package Bar is
	procedure Foo_Bar(Some_Parameter : in Type_2);
end Bar;

then in your package body:

package body Bar is
	
	procedure Foo_Bar(Some_Parameter : in Type_2) is
	begin
		.
		.
		Foo(some_other_parameter);
		.
		.
	end Foo_Bar;
end Bar;

You instantiate this with
	procedure a_procedure(a : Type_2); -- Declare your procedure
	procedure a_procedure(a : Type_2) is -- the body
	begin
		(some code)
	end a_procedure;

	package My_Bar is new Bar(A_Type,another_type,a_procedure);

Simple as that. 
It's in LRM 12.1.3, 12.3.6.

>-Julian Insan Kamil
>Computer Consultant at SUNY-Binghamton
>email: consp10@bingsunb.cc.binghamton.edu
>email: consp10@bingvaxu.cc.binghamton.edu
--
Erik Svensson			Research Officer
Guided Weapons Division		National Defense Research Establishment (FOA)
Stockholm			Sweden

net.address: 	eriks@fenix.lin.foa.se

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