On Monday, 19 May 2014 at 19:20:46 UTC, Steven Schveighoffer
wrote:
On Mon, 19 May 2014 15:03:55 -0400, Dicebot <[email protected]>
wrote:
On Monday, 19 May 2014 at 17:35:34 UTC, Steven Schveighoffer
wrote:
On Mon, 19 May 2014 13:31:08 -0400, Ola Fosheim Grøstad
<[email protected]> wrote:
On Monday, 19 May 2014 at 17:11:43 UTC, Steven Schveighoffer
wrote:
It shouldn't matter. Something that returns immutable
references, can return that same thing again if asked the
same way. Nobody should be looking at the address in any
meaningful way.
I think this is at odds with generic programming. What you
are saying is that if you plug a pure function into an
algorithm then you have to test for "pure" in the algorithm
if it is affected by object identity. Otherwise, goodbye
plug-n-play.
I think I misstated this, of course, looking at the address
for certain reasons is OK, Object identity being one of them.
immutable(Object*) alloc() pure
{
return new Object();
}
bool oops() pure
{
auto a = alloc();
auto b = alloc();
return a is b;
}
This is a snippet that will always return `true` if
memoization is at work and `false` if strongly pure function
will get actually called twice. If changing result of your
program because of silently enabled compiler optimization does
not indicate a broken compiler I don't know what does.
The code is incorrectly implemented, let me fix it:
bool oops() pure
{
return false;
}
-Steve
Oh, and are probably eager to show me links to specs which
indicate what part of my snippet breaks the type system? Is it
allocation that is forbidden in reasonable code? Or object
identity?
Please stop this "write proper code" absurdism. This code is
safe, doesn't use casts or pointer forging or any other dirty low
level tricks. If compiler can't reject it as invalid and goes
into funny mode instead, compiler is fucked. There can be no
excuse for it.
Your statement is essentially no different from "yeah this
language supports addition but please never add 3 and 6, it is
incorrect and will always return random results". Language spec
is demanded for a reason.
