[M3devel] ADR is *too* unsafe..

[Tony Hosking]

Actually, the compiler already has support to do exactly what you want.  Take a look at the flag Host.new_adr.  This implements:

ADR (t: T): UNTRACED REF T



On 2 Jun 2010, at 10:07, Jay K wrote:

> 
> The compiler doesn't break. Mentor does, networking stuff. I fixed it. But I would have
> expected the compiler to have told me about it.
> It is unfortunate. ADR should be *slightly* safer.
> Maybe we can get a warning for this? passing ADR(foo) to untraced ref bar?
> It seems...quite unfortunate that the language is defined this way..
> 
>  - Jay
> 
> 
> ----------------------------------------
>> From: hosking at cs.purdue.edu
>> Date: Wed, 2 Jun 2010 10:01:09 -0400
>> To: jay.krell at cornell.edu
>> CC: m3devel at elegosoft.com
>> Subject: Re: [M3devel] ADR is *too* unsafe..
>> 
>> Why does the compiler break?
>> Yes, VAR is *much* safer.
>> 
>> On 2 Jun 2010, at 03:41, Jay K wrote:
>> 
>>> 
>>> (*
>>> Wow, ADR generates a plain ADDRESS, not an untraced ref to a specific type?
>>> Doesn't this seem wrong? Doesn't unsafe code deserve a little better, say,
>>> to be at least as typesafe as C?
>>> http://www.cs.purdue.edu/homes/hosking/m3/reference/unsafe.html
>>> 
>>> This is why 64bit m3-comm/tcp/src/TCP.m3 breaks randomly
>>> on some platforms on an assertion failure in C. And the
>>> compiler isn't going to help me find these type mismatches? Ugh.
>>> 
>>> This seems wrong. :(
>>> 
>>> I guess I should really really use VAR then.
>>> *)
>>> 
>>> 
>>> UNSAFE MODULE Main;
>>> IMPORT Ctypes, Cstddef;
>>> 
>>> 
>>> PROCEDURE F1(a:UNTRACED REF Ctypes.int) =
>>> BEGIN
>>> F2(a); (* error, expected *)
>>> END F1;
>>> 
>>> 
>>> PROCEDURE F2(a:UNTRACED REF Cstddef.size_t) =
>>> BEGIN
>>> F1(a); (* error, expected *)
>>> END F2;
>>> 
>>> 
>>> VAR c:Ctypes.int;
>>> d:Cstddef.size_t;
>>> 
>>> 
>>> BEGIN
>>> F1(ADR(c)); (* ok *)
>>> F1(ADR(d)); (* error expected but no *)
>>> F2(ADR(c)); (* error expected but no *)
>>> F2(ADR(d)); (* ok *)
>>> END Main.
>>> 
>>> 
>>> 
>>> - Jay
>>> 
>> 
>