Comments on: Gem #62: C++ constructors and Ada 2005 http://www.adacore.com/2009/04/06/gem-62/ AdaCore technology and news Mon, 06 Feb 2012 18:59:19 -0500 http://wordpress.org/?v=2.9 hourly 1 By: Brad Moore http://www.adacore.com/2009/04/06/gem-62/comment-page-1/#comment-3558 Brad Moore Mon, 13 Apr 2009 14:42:59 +0000 http://www2.adacore.com/?p=2743#comment-3558 function New_Rec2 above, if declared as a primitive operation of type Rec2, would be a dispatching operation, and if a new type were derived from Rec2, (say Rec3) it would require that Rec3 provide an overloaded version of New_Rec2. This may not be appropriate (naming issues aside). Supposing the Rec3 type adds further discriminants. The New_Rec2 function may not be able to determine the values to use for the new discriminants of Rec3. It would be helpful to show how to declare the New_Rec2 function so that it is not inherited by derivations of Rec2. My understanding is that one of the best ways to do this is to declare such constructor functions in a nested package. This way they cannot be primitive functions, and cannot be inherited. eg package Recs is type Rec1 is limited ... type Rec2 is limited ... package Constructors is function New_Rec2 (V : Integer) return Rec2; end Constructors; end package Recs; Are there other approaches to consider? function New_Rec2 above, if declared as a primitive operation of type Rec2, would be a dispatching operation, and if a new type were derived from Rec2, (say Rec3) it would require that Rec3 provide an overloaded version of New_Rec2. This may not be appropriate (naming issues aside). Supposing the Rec3 type adds further discriminants. The New_Rec2 function may not be able to determine the values to use for the new discriminants of Rec3. It would be helpful to show how to declare the New_Rec2 function so that it is not inherited by derivations of Rec2.
My understanding is that one of the best ways to do this is to declare such constructor functions in a nested package. This way they cannot be primitive functions, and cannot be inherited. eg
package Recs is
type Rec1 is limited …
type Rec2 is limited …
package Constructors is
function New_Rec2 (V : Integer) return Rec2;
end Constructors;
end package Recs;

Are there other approaches to consider?

]]> By: Paul F. Pearson http://www.adacore.com/2009/04/06/gem-62/comment-page-1/#comment-3527 Paul F. Pearson Tue, 07 Apr 2009 18:07:55 +0000 http://www2.adacore.com/?p=2743#comment-3527 Will a future gem discuss destructors? I presume that they are handled in a similar fashion. Will a future gem discuss destructors? I presume that they are handled in a similar fashion.

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