Comments on: Using Tuples for Overriding Equality and GetHashCode

By: Steven Rothwell

Steven Rothwell — Tue, 29 Jun 2021 12:44:27 +0000

I really like this implementation. Was using it as a guide when writing my own. I found that == and != operators will throw null reference error if lhs is null. Since default implementation of == and != operators does not bomb when null, I think this should be accounted for. Similarly said for Equals(Arc arc) if arc is null. In my code, I accounted for this by utilizing a static GetHashCode(Arc arc) method.

public static Int32 GetHashCode(Arc arc)
{
if (arc is null)
return 0;

return (arc.Radius, arc.StartAngle, arc.SweepAngle).GetHashCode();
}

This allows you to simplify both Equals methods, operator methods, and non-static GetHashCode() to all call this static GetHashCode(Arc arc).

By: Eric Robishaw

Eric Robishaw — Tue, 22 Jun 2021 23:41:34 +0000

Be very careful, however. If you have 8+ items in the Tuple, the Tuple’s GetHashCode() value get’s wonky, and appears to only use the last 8 items (not the first 8)
(1, 10, “”, 2, 42, “ABC”, 723, 1000652, 4).GetHashCode() ==
(5, 10, “”, 2, 42, “ABC”, 723, 1000652, 4).GetHashCode()

(1, 10, “”, 2, 42, “ABC”, 723, 1000652).GetHashCode().Dump() !=
(5, 10, “”, 2, 42, “ABC”, 723, 1000652).GetHashCode().Dump()

(5, 10, “”, 2, 42, “ABC”, 723, 1000652, 2).GetHashCode().Dump() !=
(5, 10, “”, 2, 42, “ABC”, 723, 1000652, 3).GetHashCode().Dump();

By: Kevin Bost

Kevin Bost — Fri, 15 Nov 2019 17:47:59 +0000

In reply to PAUL G MILLER.

When you do (Radius, StartAngle, SweetAngle) it creates a System.ValueTuple and invokes the GetHashCode function of it. ValueTuple’s GetHashCode method will combine the hash codes of each of its members to produce a file hash code.

https://source.dot.net/#System.Private.CoreLib/shared/System/ValueTuple.cs,763

By: PAUL G MILLER

PAUL G MILLER — Fri, 23 Aug 2019 22:27:00 +0000

public override int GetHashCode() => return (Radius, StartAngle, SweepAngle).GetHashCode();
will just return Radius.GetHashCode() so that’s probably not what you want.

https://github.com/dotnet/coreclr/blob/4aa65f077778c7c05211825f98684aae9c52caaf/src/System.Private.CoreLib/shared/System/Tuple.cs