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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Introductory Presentations, especially aimed at C++ programmers!
Date: Tue, 13 Dec 2016 17:05:53 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:32798
Date: 2016-12-13T17:05:53-06:00
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"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:o2pr84$fis$1@dont-email.me...
...
>    return Buffer & Get_Line;

This does dynamic allocation of some sort under the covers, and in any case 
copies the contents of both parts of the string. The version Bob shows is 
more complicated in order to control the amount of stack space used, and 
appears to be designed to maximize the use of stack space rather than 
allocated temporaries for GNAT. That seems like a win for their 
implementation.

In Janus/Ada, both of these formulations would do a heck of a lot of dynamic 
allocation under the covers (anything dynamically sized is allocated from a 
storage pool ultimately). [That's what I was thinking of when I said 
"dynamically allocated".] & of unconstrained strings is VERY expensive, so I 
would write a routine similar to the one Bob showed, but I'd use slicing 
rather than & to create the final result. (Given the general nature of 
Get_Line, and the way it is used, it will be on some program's critical 
path, so it can never be fast enough.) [I used future tense as this 
particular Ada 2005 change hasn't yet made it into Janus/Ada.]

Conclusion: I don't see any difference between Bob's version and yours in 
terms of dynamic memory allocation needed.

                                      Randy.