From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	ip-172-31-65-14.ec2.internal
X-Spam-Level: 
X-Spam-Status: No, score=-0.0 required=3.0 tests=BAYES_20,T_SCC_BODY_TEXT_LINE,
	XPRIO autolearn=ham autolearn_force=no version=3.4.6
Path: eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Why don't all initialising assignments use 'build-in-place' ?
Date: Sat, 25 Mar 2023 03:39:14 -0500
Organization: A noiseless patient Spider
Message-ID: <tvmbvj$2417c$1@dont-email.me>
References: <tvc6j9$3gfe$1@dont-email.me>
Injection-Date: Sat, 25 Mar 2023 08:39:15 -0000 (UTC)
Injection-Info: dont-email.me; posting-host="6687f069bfe0f361727be044aacd443a";
	logging-data="2229484"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX18iJzcbYF/pyabp8jhnBOyW6ZJkJfqWToY="
Cancel-Lock: sha1:UBIcAN2ldIRYBPasPOa1lb+WSyk=
X-RFC2646: Format=Flowed; Response
X-Priority: 3
X-MSMail-Priority: Normal
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.7246
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
Xref: feeder.eternal-september.org comp.lang.ada:65019
List-Id: <comp.lang.ada>

"Rod Kay" <rodakay5@gmail.com> wrote in message 
news:tvc6j9$3gfe$1@dont-email.me...
> Hello again,
>
>    I'm sure there must be a good reason. All I can think of is that it may 
> somehow break backwards compatibility wrt controlled types (a vague stab 
> in the dark).
>
>    Any thoughts ?

(1) Didn't want to make work for implementers.
(2) You shouldn't be able to tell (since it is required for all cases 
involved finalization). Finalization is the only way to inject user-defined 
code into the initialization process.
(3) True build-in-place can be expensive and complex (especially for array 
types).
(4) Build-in-place requires functions compiled to support it (must pass in 
the place to initialize into). That might not be the case (especially if a 
foreign convention is involved). Also see (3) - an implementation might have 
a cheaper way to return some types that doesn't support build-in-place.

There's probably more, those are off the top of my head. If it is cheap, it 
would be silly for an implementation to do anything else. (Don't ask what 
Janus/Ada does. ;-) Otherwise, most people want the fastest possible code.

                       Randy.