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Newsgroups: comp.lang.ada
Date: Wed, 2 Sep 2020 21:30:16 -0700 (PDT)
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Subject: Re: Proposal: Auto-allocation of Indefinite Objects
From: linda white <lindaqwhite1@gmail.com>
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On Saturday, 4 April 2020 04:18:43 UTC+5:30, Stephen Davies  wrote:
> Firstly, apologies if this has already been discussed or,
> more likely, if it's a really stupid idea for some reason
> that I haven't thought of.
> 
> My proposal is that it should (sometimes?) be possible to declare
> objects of indefinite types such as String and have the compiler
> automatically declare the space for them without the programmer
> having to resort to access types.
> 
> Benefits:
> 
> 1. Easier, especially for newbies/students.
> 2. Safer due to reduced use of access types.
> 3. Remove the need to have definite and indefinite verions of generic units.
> 
> It is the 3rd reason that initially got me thinking about this.
> It seems excessive to have two versions of packages just because
> one version can say "Node.Item := New_Item;" but the other has to say
> "Node.Item_Ptr := new Element_Type'(New_Item);".
> 
> It's probably not a good idea for auto-allocation to be the default
> behaviour, so I suggest something like:
> 
>    type Node_Type is record
>       Item : new Element_Type;
>       Prev : Node_Ptr_Type;
>       Next : Node_Ptr_Type;
>    end record;
> 
> If Element_Type is a definite type in the instantiation then
> Node.Item will be a normal object of that type. Otherwise, it is
> implemented as a pointer but the code still treats it as an object.
> The target of the pointer is allocated on assignment of the object.
> The pointer cannot be copied to any other object. Assignments of the
> whole record will perform a deep-copy of the auto-allocated component.
> The target of the Node.Item pointer can be auto-deallocated when Node
> goes out of scope or is deallocated.
> 
> Ok, I've probably missed something obvious and have been wasting my
> time, but at least I've got plenty of time to waste at the moment.