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From: "Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>
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Subject: Re: Is this a compiler bug ?
Date: Sun, 19 Mar 2023 11:33:50 +0100
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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).

-- 
Jeff Carter
"Since I strongly believe that overpopulation is by
far the greatest problem in the world, this [Soylent
Green] would be my only message movie."
Charleton Heston
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