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Newsgroups: comp.lang.ada
Date: Sat, 1 Aug 2020 13:35:32 -0700 (PDT)
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Subject: Re: Proposal: Auto-allocation of Indefinite Objects
From: Stephen Davies <joviangm@gmail.com>
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On Saturday, 1 August 2020 at 13:58:10 UTC+1, Dmitry A. Kazakov wrote:
> On 01/08/2020 13:22, Stephen Davies wrote: 
> > type Node_Type (<>) is record 
> > Item : Element_Type; 
> > Prev : Node_Ptr_Type; 
> > Next : Node_Ptr_Type; 
> > end record; 
> > The rules for such records would be the same as for discriminated ones, 
> > except that instead of usages needing to provide values for discriminants, 
> > they would need to provide values for indefinite components.
> 1. There is no discriminants for cases when Item is T'Class. 
> 2. You cannot get discriminant from the value in the case of Rosen trick...
> 3. Copying is involved. There should be none, especially for limited types...
I'm mainly talking about situations in which there doesn't need to be a
discriminant at all, e.g. when Element_Type is an indefinite non-limited
generic parameter. In other words, Node_Type would then also be indefinite,
but not discriminated.
> Why not to make this legal?
> X : T := ("hello!", 123); -- L is deduced from S
Maybe that's something that should be fixed anyway, though this is indeed
another situation that (both versions of) my proposal would address, by
removing (the somewhat redundant) L altogether.