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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Allocators and the requirement to raise `Storage_Error`
Date: Fri, 3 May 2013 18:17:02 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-05-03T18:17:02-05:00
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"Yannick Duch�ne (Hibou57)" <yannick_duchene@yahoo.fr> wrote in message 
news:op.wwh16wl5ule2fv@cardamome...
...
>I still wonder why there is no provision for an allocator to return `null` 
>instead of raising an exception, when a custom function of a constrained 
>subtype/type, which would provide the same functionality, does not get 
>imposed this obligation.

This seems like a bizarre question. Ada doesn't allow returning the wrong 
answer from an operation; it's required to return the right answer or an 
exception. The operation "new" returns an allocated object. Period. If that 
can't be done, then an exception is raised immediately.

Not doing this would hide storage exhaustion and would make it look like an 
ordinary bug. That would make it a lot harder to reason about programs (its 
very hard to reason about storage exhaustion, it formally can happen 
anywhere, even "null;"). Keeping them separate helps both debugging and 
formal tools.

                                     Randy.