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From: Robert A Duff <bobduff@TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Introductory Presentations, especially aimed at C++ programmers!
Date: Tue, 13 Dec 2016 17:52:05 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2016-12-13T17:52:05-05:00
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"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:

> Yes, but the GNAT implementation is rather poor.

It depends on whether you care about very long lines.
If so, you want to double the buffer size each time
(or similar).

If the line is a million characters, the GNAT version
does around 20 recursive calls, whereas the version below
does around 1000 recursive calls.

I'm too lazy to measure the speed, and anyway, the computation might be
swamped by the disk access.  Text_IO should be (should have been!)
designed for convenience, not efficiency.  You don't call Text_IO
in the inner loops of an embedded real-time system.  ;-)

>... A better way doesn't
> need to copy anything:

You can't do "return Buffer & Get_Line;" without some copying.
I'm willing to believe that GNAT does more copying than is
absolutely necessary.

> function Get_Line return String is
>    Buffer : String (1 .. 1_000);
>    Last   : Natural;
> begin -- Get_Line
>    Get_Line (Item => Buffer, Last => Last);
>
>    if Last < Buffer'Last then
>       return Buffer (1 .. Last);
>    end if;
>
>    return Buffer & Get_Line;
> end Get_Line;

- Bob