[Issue 17206] Checks that opEquals and toHash are both defined or neither are defined

Mar 28, 2018

https://issues.dlang.org/show_bug.cgi?id=17206 Jack Stouffer <jack@jackstouffer.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Depends on| |18674, 18675, 18676, 18677, | |18678 Referenced Issues: https://issues.dlang.org/show_bug.cgi?id=18674 [Issue 18674] std.json.JSONValue has opEquals but no toHash https://issues.dlang.org/show_bug.cgi?id=18675 [Issue 18675] std.experimental.checkedint.Checked has opEquals but no toHash https://issues.dlang.org/show_bug.cgi?id=18676 [Issue 18676] std.datetime.date.DateTime has opEquals but no toHash https://issues.dlang.org/show_bug.cgi?id=18677 [Issue 18677] std.datetime.date.Date has opCmp but no toHash https://issues.dlang.org/show_bug.cgi?id=18678 [Issue 18678] std.datetime.date.TimeOfDay has opCmp but no toHash --

March 28, 2018

[Issue 17206] [Tracking] Check that opEquals and toHash are both defined or neither are defined

Posted by Jack Stouffer

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Jack Stouffer

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https://issues.dlang.org/show_bug.cgi?id=17206

Jack Stouffer <jack@jackstouffer.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Depends on|                            |18679, 18680, 18681, 18682,
                   |                            |18683, 18684, 18685, 18686,
                   |                            |18687
            Summary|Checks that opEquals and    |[Tracking] Check that
                   |toHash are both defined or  |opEquals and toHash are
                   |neither are defined         |both defined or neither are
                   |                            |defined


Referenced Issues:

https://issues.dlang.org/show_bug.cgi?id=18679
[Issue 18679] std.complex.opEquals has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18680
[Issue 18680] std.random.LinearCongruentialEngine has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18681
[Issue 18681] std.random.XorshiftEngine has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18682
[Issue 18682] std.typecons.Nullable has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18683
[Issue 18683] std.containers.rbtree.RedBlackTree has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18684
[Issue 18684] std.containers.array.Array has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18685
[Issue 18685] std.containers.slist.SList has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18686
[Issue 18686] std.containers.dlist.DList has opEquals but no toHash
https://issues.dlang.org/show_bug.cgi?id=18687
[Issue 18687] std.numeric.CustomFloat has opEquals but no toHash
--

https://issues.dlang.org/show_bug.cgi?id=17206 Issue 17206 depends on issue 18678, which changed state. Issue 18678 Summary: std.datetime.date.TimeOfDay has opCmp but no toHash https://issues.dlang.org/show_bug.cgi?id=18678 What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |INVALID --

https://issues.dlang.org/show_bug.cgi?id=17206 Issue 17206 depends on issue 18677, which changed state. Issue 18677 Summary: std.datetime.date.Date has opCmp but no toHash https://issues.dlang.org/show_bug.cgi?id=18677 What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |INVALID --

https://issues.dlang.org/show_bug.cgi?id=17206 Issue 17206 depends on issue 18676, which changed state. Issue 18676 Summary: std.datetime.date.DateTime has opCmp but no toHash https://issues.dlang.org/show_bug.cgi?id=18676 What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution|--- |INVALID --

https://issues.dlang.org/show_bug.cgi?id=17206 Nathan S. <n8sh.secondary@hotmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |n8sh.secondary@hotmail.com --- Comment #2 from Nathan S. <n8sh.secondary@hotmail.com> --- Half of this is wrong. For a type to be usable as a key in an associative array it must be true that "a == b" implies "a.toHash() == b.toHash()", so when there is a non-default `==` there should also be a custom `toHash` to maintain this property. But the reverse is not true: defining a non-default `toHash` does not require a custom `opEquals`, because the default `==` is already the strictest possible condition that satisfies "a == a" (since structs can be relocated). --

https://issues.dlang.org/show_bug.cgi?id=17206 Steven Schveighoffer <schveiguy@yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |schveiguy@yahoo.com --- Comment #3 from Steven Schveighoffer <schveiguy@yahoo.com> --- No, toHash doesn't necessarily have to follow the semantics of default opEquals. Example: struct S1(bool customTohash) { string s; static if(customTohash) { size_t toHash() const { return cast(size_t)s.ptr + s.length; // use string identity } /+ really should define this bool opEquals(const(S1) other) const { return other.s is s; } +/ } } void main() { bool[S1!false] aa1; aa1[S1!false("hello".idup)] = true; aa1[S1!false("hello".idup)] = true; assert(aa1.length == 1); bool[S1!true] aa2; aa2[S1!true("hello".idup)] = true; aa2[S1!true("hello".idup)] = true; assert(aa2.length == 1); // fails } --

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