Date: Fri, 15 Oct 1999 08:43:54 +1000
From: skaller <skaller@maxtal.com.au>
To: Manuel Fahndrich <maf@microsoft.com>
Subject: Re: Proposal for study: Add a categorical Initial type to ocaml
Manuel Fahndrich wrote:
>
> skaller wrote:
>
> [...]
>
> > Like I've been saying, with option you can turn it off, with
> Obj.magic, the implementor ought to be damned sure he's doing things right.
> But with these special "uninitialized value" sorts of things, people like
> me who've gotten used to good type systems keep looking over their
> shoulders because they're afraid it might turn around and bite
> them in the butt.
>
>> How is this different from Obj.magic? Can't that bite you
>> in the ass too?
>
>>> The difference is that in the first case of uninitialized values, they can
>>> crop up anywhere in your program, since they get propagated. Using Obj.magic
>>> within a special module such as resizable arrays confines the danger to that
>>> module. The programmer can make sure (through extensive code reviews of a
>>> finite piece of code) that outside the module, things cannot go awry.
No. It is the other way around. Obj.magic values can get
propagated, and so cause a problem. The special initial can NOT
be propagated. Any attempt to copy such a value raises an exception.
Ensuing this does not happen is also a matter of hiding within
a modular abstraction, but at least an exception will help
detect such localised errors.
-- John Skaller, mailto:skaller@maxtal.com.au 1/10 Toxteth Rd Glebe NSW 2037 Australia homepage: http://www.maxtal.com.au/~skaller downloads: http://www.triode.net.au/~skaller
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