🚀 go-pugleaf

maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes:

>However, lets consider that Unix file names are 'pointers' to files,
>and that links are allowed.
>
>Then the average program cant tell if two file names point to
>the same file or not, since computing the inode number is the only
>way to do that, and only super users can do this calculation.
>(Imagine I'm right even if this isnt the case. Is it the case?)

No. Computing the inode number is not a privileged operation.

>Would this make such a system 'unworkable'?

Not if the system had mandatory (as opposed to advisory) locks.

>The issue is whether pointers must provide any more functionality
>than the ability to access an object, that is, whether object
>identity can be established by pointer comparisons.

Like it or not (in many ways I don't!), it seems that this principle
is firmly entrenched in C++. Consider the requirement 
empty classes must have non-zero sizes, etc.

>I suggest that whole classes of software can be written that 
>do not rely on the ability to test if two pointers refer
>to the same object or not, other types of software require
>this information.
>
>Perhaps we can conceive two types of pointers, type 1 
>provides no comparisons at all, type 2 allows equality test.
>
>Most of the code I've written uses type 1, and most uses
>of type 2 could be rewritten as type 1.

Equality tests are often needed in assignment operators, to
check for the special case of x=x.

>In those cases where type 2 pointers are desirable, it
>seems reasonable to restrict them to pointers
>to objects created directly by me, and not the operating
>system.
>
>Thus I would like to see the ARM == rewritten so the
>results of == on externally derived or otherwise mangled
>pointers are implementation defined.

As I said in a previous post, I think that this is already
the case for C, and I expect it to be the same for C++
when the ANSI or ISO C++ standard finally comes out.
Once you have invoked the operating system, all bets are off.

-- 
Fergus Henderson             fjh@munta.cs.mu.OZ.AU      
This .signature virus is a self-referential statement that is true - but 
you will only be able to consistently believe it if you copy it to your own
.signature file!