[M3devel] subranges 0..-1?

[Jay K]

So, I'm not supposed to worry about unsafe stuff..including if the backend and debugging information can  handle it? No.
Unsafe code matters, a lot.

 - Jay

----------------------------------------
> To: jay.krell at cornell.edu
> Date: Mon, 4 Oct 2010 11:12:08 -0700
> From: mika at async.async.caltech.edu
> CC: m3devel at elegosoft.com
> Subject: Re: [M3devel] subranges 0..-1?
>
> Jay K writes:
> >
> >It worries me somewhat that we allow zero-sized types.
> >Including TYPE Foo =3D RECORD END=3B
> >It is reassuring to me that C and C++ doesn't have these.
> >I don't want to think about what they mean.
> >Do they make sense to others?
>
> Yes, they make a lot of sense. Not having them means special-casing
> any program that generates code. Obviously a correct program that generates
> code including a zero-sized array will never generate an expression
> that indexes such an array...
>
> >
> >C requires a field. C++ adds a dummy one internally=2C that it can/must try
> >to optimize away when inheritance is involved but still.
> >
> >
> >C++ is interested in the property of pointers not being equal=2C like:
> >
> >TYPE T1 =3D RECORD END=3B
> >TYPE T2 =3D RECORD a=2Cb:T1 END=3B
> >
> >VAR a:T1=3B
> >ADR(a.b) # ADR(a.a.)=3B
> >
> >But in Modula-3 they would have the same address.
> >What does it mean to take the address of something that doesn't exist?
> >Perhaps it isn't allowed?
>
> This is UNSAFE code, so it means whatever the implementation makes
> it mean, including (as far as I'm concerned) a compiler crash, if
> that is the easiest thing you can make it mean. I really wouldn't
> worry about the UNSAFE parts of Modula-3 that much... expected to be
> implementation-dependent. Although I admit it would be better to have
> it do something meaningless in this case. Since T1 is an empty type
> there's not much you can do with the address anyhow.
>
> Mika