[Issue 14804] Comparing two Nullables does not check if either is null

Dec 25, 2015

b2.temp@gmx.com

Dec 27, 2015

monkeyworks12@hotmail.com

Dec 28, 2015

Jan 23, 2016

Mar 30, 2016

Apr 05, 2016

Mar 21, 2020

https://issues.dlang.org/show_bug.cgi?id=14804 b2.temp@gmx.com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |b2.temp@gmx.com --- Comment #1 from b2.temp@gmx.com --- I was about to propose a PR that changes the behavior of Nullable but actually I think your report is invalid: 1/ it only throws in asseert mode, which allows to detect a wrong usage when testing the software and maybe to add some isNull() before comparing if necessary. 2/ if a custom opEquals() is added, even if it works fine, it becomes quite unclear how opCmp() should behave then. see the changes: https://github.com/BBasile/phobos/commit/f458ad1318e5536c91882c02397df262961c63a2#diff-4e008aedb3026d4a84f58323e53bf017R1930 so I suggest you to close. --

December 27, 2015

[Issue 14804] Comparing two Nullables does not check if either is null

Posted by monkeyworks12@hotmail.com

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monkeyworks12@hotmail.com

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https://issues.dlang.org/show_bug.cgi?id=14804

--- Comment #2 from monkeyworks12@hotmail.com ---
I agree opCmp is a little weird to implement for Nullable, but it's really not much different from NaN. If we follow what the floating point numbers do:

Nullable!int n1;
Nullable!int n2 = 0;

assert(!(n1 < n2) && !(n1 == n2) && !(n1 > n2));

Of course the semantics of NaN are somewhat confusing at first and possibly bug-prone, so it may not be something we want to duplicate in another type if possible. Interestingly, this is how the built-in "nullable" types behave when compared:

    Object o1 = null;
    Object o2 = new Object();
    assert(o1 > o2); //Segfault

    int* i1 = null;
    int* i2 = new int(0);
    assert(i1 <= i2); //One of these will pass
    assert(i1 > i2);

    int[] a1 = null;
    int[] a2 = [0];
    assert(a1 <= a2); //I didn't know this was valid code;
    assert(a1 > a2);  //it must compare the array pointers
                          //and thus work similarly to case 2

So it looks like we have our choice of semantics to choose from.


Either way, the issue of opCmp is completely separate from opEquals, so I don't agree that this bug should be closed. Every built-in nullable type in D works as I described, and I don't believe that Nullable should be any different.

Object o1 = null;
Object o2 = new Object();
assert(o1 != o2); //Passes

int* i1 = null;
int* i2 = new int(0);
assert(i1 != i2); //Passes

int[] a1 = null;
int[] a2 = [0];
assert(a1 != a2); //Passes


The fact that these issues pop up when you actually try to use Nullable in any serious way suggest to me that its design is deeply flawed, and that it should be deprecated and replaced at some point. However, until that happens, we should aim to improve it as much as possible without breaking existing code.

If you don't want to open a defect for Nullable.opCmp, that's fine with me, but let's not close this one for opEquals.

--

https://issues.dlang.org/show_bug.cgi?id=14804 --- Comment #3 from b2.temp@gmx.com --- (In reply to monkeyworks12 from comment #2) > but let's not close this one for opEquals. Without great convictionI've opened the PR, but let's the official maintainers take the decision ;) https://github.com/D-Programming-Language/phobos/pull/3887 --

https://issues.dlang.org/show_bug.cgi?id=14804 Luís Marques <luis@luismarques.eu> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |luis@luismarques.eu --- Comment #4 from Luís Marques <luis@luismarques.eu> --- I've also stumbled on this limitation, but the behavior I was looking forward to was: Nullable!int a; Nullable!int b; assert(a == b); Nullable!int c; Nullable!int d = 42; assert(c != d); Since I can see the benefit of using Nullable in these different ways, that probably means this should be a template parameter. --

https://issues.dlang.org/show_bug.cgi?id=14804 Jack Stouffer <jack@jackstouffer.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED CC| |jack@jackstouffer.com Resolution|--- |DUPLICATE --- Comment #5 from Jack Stouffer <jack@jackstouffer.com> --- *** This issue has been marked as a duplicate of issue 13017 *** --

https://issues.dlang.org/show_bug.cgi?id=14804 Basile-z <b2.temp@gmx.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC|b2.temp@gmx.com | --

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