On Thursday, 15 May 2014 at 06:50:06 UTC, Ola Fosheim Grøstad
wrote:
On Thursday, 15 May 2014 at 06:29:06 UTC, bearophile wrote:
A little example of D purity (this compiles):
bool randomBit() pure nothrow @safe {
return (new int[1].ptr) > (new int[1].ptr);
}
Yes, and then you may as well allow a random generator with
private globals. Because memoing is no longer sound anyway.
No, this particular example appears to be invalid code. Under the
C memory model [1], the result of comparing two pointers to
distinct objects (allocations) is undefined/unspecified behavior
(I think it is undefined in C and unspecified in C++, but I don't
remember the details).
Of course, you could rescue the example by casting the pointers
to size_t or something along the lines, but this is something
that could be disallowed in pure code.
David
[1] Which typically applies to D, unless defined otherwise. Our
language specification is woefully incomplete in this regard,
though.
