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The GetHashCode implementation of the Thickness struct is broken for uniform length. #8789

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davidskula opened this issue Feb 8, 2024 · 1 comment · May be fixed by #8822
Open

The GetHashCode implementation of the Thickness struct is broken for uniform length. #8789

davidskula opened this issue Feb 8, 2024 · 1 comment · May be fixed by #8822
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🚧 work in progress Investigate Requires further investigation by the WPF team.

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@davidskula
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Description

For any uniform length instance of Thickness struct GetHashCode returns zero.

Reproduction Steps

var h1 = new Thickness(5).GetHashCode();
var h2 = new Thickness(10).GetHashCode();

Expected behavior

h1 and h2 should have different values

Actual behavior

h1 and h2 have the same value

Regression?

No response

Known Workarounds

No response

Impact

No response

Configuration

No response

Other information

No response
@singhashish-wpf singhashish-wpf added the Investigate Requires further investigation by the WPF team. label Feb 9, 2024
@lindexi
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lindexi commented Feb 18, 2024 •
edited

The reason is:

wpf/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Thickness.cs

Lines 96 to 99 in 19f227f

public override int GetHashCode()
{
return _Left.GetHashCode() ^ _Top.GetHashCode() ^ _Right.GetHashCode() ^ _Bottom.GetHashCode();
}

The uniform length means that the _left == _Top == _Right == _Bottom. And the same value call the GetHashCode will return the same result. And the two same value call the ^ will return zero.

I'm not sure I can change its behavior.

lindexi added a commit to dotnet-campus/wpf that referenced this issue Feb 18, 2024
@lindexi
Try fix GetHashCode implementation of the Thickness struct is broken …
9b8fade 
…for uniform length

dotnet#8789
@lindexi lindexi linked a pull request Feb 18, 2024 that will close this issue
Open
lindexi added a commit to dotnet-campus/wpf that referenced this issue Feb 18, 2024
@lindexi
Try fix GetHashCode implementation of the Thickness struct is broken …
736f6f5 
…for uniform length

dotnet#8789
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@davidskula @lindexi @singhashish-wpf