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From: Rod Kay <rodakay5@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Is this a compiler bug ?
Date: Mon, 20 Mar 2023 13:24:40 +1100
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On 19/3/23 21:33, Jeffrey R.Carter wrote:
> On 2023-03-19 07:17, Rod Kay wrote:
>>
>>     In the 'to_Stack' function, the Capacity is reserved correctly but 
>> in the test program when the stack is created and assigned to a 
>> variable, the capacity is 0.
> 
> I think this is acceptable behavior. See ARM A.18.2 (147.19/3, 147.20/3, 
> & 147.b/3) 
> (http://www.ada-auth.org/standards/aarm12_w_tc1/html/AA-A-18-2.html). 
> The first two sections define the behavior of procedure Assign, while 
> the last states "Assign(A, B) and A := B behave identically".
> 
> Assign (A, B) only changes the capacity of A if A.Capacity < B.Length.
> 
> So if the compiler does not use build-in-place for the initialization of 
> the variable, then the assignment of the function result should not 
> change the capacity of the variable from its (apparent) default of zero 
> (there is, of course, no requirement for the capacity of a 
> default-initialized vector).
> 
> The discussion of capacities for vectors is only meaningful for a subset 
> of possible implementations, so messing with capacities may have no 
> meaningful effect at all.
> 
> For an unbounded stack based on a linked list (with no concept of 
> capacity) you could use 
> PragmARC.Data_Structures.Stacks.Unbounded.Unprotected 
> (https://github.com/jrcarter/PragmARC/blob/Ada-12/pragmarc-data_structures-stacks-unbounded-unprotected.ads).
> 


    Thank you, Jeffrey, for the detailed reply.

    I'm now using a limited record with an extended return for 
'build-in-place' initialisation and am getting the behavior I desired.


Cheers.