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

[d-bugmail--- via Digitalmars-d-bugs]

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

Basile-z  changed:

   What|Removed |Added

 CC|b2.t...@gmx.com |

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

[via Digitalmars-d-bugs]

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

Jack Stouffer  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 CC||j...@jackstouffer.com
 Resolution|--- |DUPLICATE

--- Comment #5 from Jack Stouffer  ---


*** This issue has been marked as a duplicate of issue 13017 ***

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

[via Digitalmars-d-bugs]

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

Luís Marques  changed:

   What|Removed |Added

 CC||l...@luismarques.eu

--- Comment #4 from Luís Marques  ---
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.

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

[via Digitalmars-d-bugs]

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

b2.t...@gmx.com changed:

   What|Removed |Added

   See Also||https://issues.dlang.org/sh
   ||ow_bug.cgi?id=10771

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

[via Digitalmars-d-bugs]

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

--- Comment #3 from b2.t...@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

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

[via Digitalmars-d-bugs]

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

--- Comment #2 from monkeywork...@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.

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

[via Digitalmars-d-bugs]

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

b2.t...@gmx.com changed:

   What|Removed |Added

 CC||b2.t...@gmx.com

--- Comment #1 from b2.t...@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.

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