.GetHashCode() should not report the same value for all instances of [pscustomobject]

[mklement0]

Prerequisites

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Steps to reproduce

[pscustomobject] is a reference type without overridden equality-comparison behavior, so testing for equality performs reference equality, i.e. the test only succeeds if to values point to the very same instance.

Such types usually use the default (inherited) .GetHashCode() implementation, which for reference types means a value that is derived from the instance's identity.

Unexpectedly, all [pscustomobject] instances return the same from their .GetHashCode() method, which makes [pscustomobject] unsuitable as a hashtable key, for instance.

Expected behavior

PS> ([pscustomobject] @{ foo=1 }).GetHashCode() -eq ([pscustomobject] @{ foo=1 }).GetHashCode()
False # Two distinct [pscustomobject] instances that compare unequally should have distinct hash codes.

Actual behavior

The above returns $true, even though [pscustomobject] @{ foo=1 } -eq [pscustomobject] @{ foo=1 } returns $false (due to reference equality being tested).

Error details

No response

Environment data

PowerShell Core 7.2.0-preview.7

Visuals

No response

[vexx32]

I'm wondering if we should define a hash code based on the identifying components of a PSCustomObject 🤔

I'm thinking perhaps something combining hashcode values from:

• Property names
• Property values
• PSTypeNames
• Any other added member names / type signatures(?)

[SeeminglyScience]

It's typically advised to not make hash codes based on members if they aren't immutable (messes with dictionary look ups).

PSObject.GetHashCode should be something like this:

public override int GetHashCode()
{
    return BaseObject is PSCustomObject ? base.GetHashCode() : BaseObject.GetHashCode();
}

[microsoft-github-policy-service]

This issue has not had any activity in 6 months, if this is a bug please try to reproduce on the latest version of PowerShell and reopen a new issue and reference this issue if this is still a blocker for you.

[microsoft-github-policy-service]

This issue has not had any activity in 6 months, if this is a bug please try to reproduce on the latest version of PowerShell and reopen a new issue and reference this issue if this is still a blocker for you.

[microsoft-github-policy-service]

This issue has not had any activity in 6 months, if this is a bug please try to reproduce on the latest version of PowerShell and reopen a new issue and reference this issue if this is still a blocker for you.

[microsoft-github-policy-service]

This issue has been marked as "No Activity" as there has been no activity for 6 months. It has been closed for housekeeping purposes.

[dkaszews]

Why is this closed? It has been waiting on the WG engine. It is ridiculous how maintainers just bot everything closed instead of actually look at the issues in questions.