Null member access operators `?.` and `?[]` by adityapatwardhan · Pull Request #10960 · PowerShell/PowerShell · GitHub

PR Summary

PR for ?. and ?[] operators.
Braces need around variable name. Like ${x}?.Name and ${x}?.Get()
Implementation on RFC - PowerShell/PowerShell-RFC#223

PR Context

The null conditional member access operators allow to check the item for being null before a property is accessed or an index is used or a method is invoked. This helps reduced the null checking logic from scripts.

PR Checklist

PR has a meaningful title
- Use the present tense and imperative mood when describing your changes
Summarized changes
Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
This PR is ready to merge and is not Work in Progress.
- If the PR is work in progress, please add the prefix WIP: or [ WIP ] to the beginning of the title (the WIP bot will keep its status check at Pending while the prefix is present) and remove the prefix when the PR is ready.
Breaking changes
- None
- OR
- Experimental feature(s) needed
  - Experimental feature name(s):
User-facing changes
- Not Applicable
- OR
- Documentation needed
  - Issue filed: Add documentation for ?? ??= ?. and ?[] operators MicrosoftDocs/PowerShell-Docs#4925
Testing - New and feature
- N/A or can only be tested interactively
- OR
- Make sure you've added a new test if existing tests do not effectively test the code changed
Tooling
- I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
- OR
- I have considered the user experience from a tooling perspective and enumerated concerns in the summary. This may include:
  - Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode (which runs in a different PS Host).
  - Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
  - Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
  - Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).
    - Filed issue: Possible update to syntax highlighting for ?? ??= ?. ?[] operators EditorSyntax#185

PoshChan-Bot (@PoshChan) please retry Windows

Aditya Patwardhan (@adityapatwardhan), successfully started retry of PowerShell-CI-Windows

Remove trailing spaces here.

Fixed

Not fixed yet.

In C#, there is no point to support ?. for member access to static members, but in PowerShell, you can do $a = [string]; $a::Equals(...), which makes it debatable whether we want to support it.

Though it is technically possible to implement something like: $a = [string]; ${a}?::Equals(...), i doubt there is any usefulness to this.

Yeah, it's technically possible. I vote for postponing it until we have a ask. Steve Lee (@SteveL-MSFT) any thoughts?

Though it is technically possible to implement something like: $a = [string]; ${a}?::Equals(...), i doubt there is any usefulness to this.

Where I think it would be most useful is situations where you want to invoke a static method only if an assembly is already loaded. e.g.

('MyCustomType' -as [type])?::Initialize()

That certainly beats my current method! (and has better utility, probably, as well)

switch ($null) {
    ('typename' -as [type]) { . Type.ps1 }
    ('type2name' -as [type]) { . Type2.ps1 }
}

Since it's additive we can postpone

Dongbo Wang (@daxian-dbw) - Please re-review.

Not fixed yet.

Rob Holt (@rjmholt) and James Truher (@JamesWTruher) Can you please review this PR as well? Thanks!

Aditya Patwardhan (@adityapatwardhan), your last commit had 1 failures in PowerShell-CI-windows
Enter-PSHostProcess tests.By Process Id.Can enter using NamedPipeConnectionInfo

Exception calling "Invoke" with "0" argument(s): "The runspace state is not valid for this operation."
at <ScriptBlock>, D:\a\1\s\test\powershell\Modules\Microsoft.PowerShell.Core\Enter-PSHostProcess.Tests.ps1: line 136
136:                 $ps.AddScript('$pid').Invoke() | Should -Be $pwshId

Aditya Patwardhan (@adityapatwardhan), your last commit had 1 failures in PowerShell-CI-windows
NullConditionalMemberAccess.?. operator tests.Use ?. on a dynamic method name that does not exist

Expected an exception, with FullyQualifiedErrorId 'Argument' to be thrown, but the FullyQualifiedErrorId was 'MethodNotFound'. from D:\a\1\s\test\powershell\Language\Operators\NullConditional.Tests.ps1:343 char:15
    +             { (Get-Date '11/11/2019')?.$methodName() } | Should -Thro ?
    +               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
at <ScriptBlock>, D:\a\1\s\test\powershell\Language\Operators\NullConditional.Tests.ps1: line 343
343:             { (Get-Date '11/11/2019')?.$methodName() } | Should -Throw -ErrorId 'Argument'

Aditya Patwardhan (@adityapatwardhan), your last commit had 1 failures in PowerShell-CI-linux
NullConditionalMemberAccess.?. operator tests.Use ?. on a dynamic method name that does not exist

Expected an exception, with FullyQualifiedErrorId 'Argument' to be thrown, but the FullyQualifiedErrorId was 'MethodNotFound'. from /home/vsts/work/1/s/test/powershell/Language/Operators/NullConditional.Tests.ps1:343 char:15
    +             { (Get-Date '11/11/2019')?.$methodName() } | Should -Thro ?
    +               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
at <ScriptBlock>, /home/vsts/work/1/s/test/powershell/Language/Operators/NullConditional.Tests.ps1: line 343
343:             { (Get-Date '11/11/2019')?.$methodName() } | Should -Throw -ErrorId 'Argument'

Aditya Patwardhan (@adityapatwardhan), your last commit had 1 failures in PowerShell-CI-macos
NullConditionalMemberAccess.?. operator tests.Use ?. on a dynamic method name that does not exist

Expected an exception, with FullyQualifiedErrorId 'Argument' to be thrown, but the FullyQualifiedErrorId was 'MethodNotFound'. from /Users/runner/runners/2.160.0/work/1/s/test/powershell/Language/Operators/NullConditional.Tests.ps1:343 char:15
    +             { (Get-Date '11/11/2019')?.$methodName() } | Should -Thro ?
    +               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
at <ScriptBlock>, /Users/runner/runners/2.160.0/work/1/s/test/powershell/Language/Operators/NullConditional.Tests.ps1: line 343
343:             { (Get-Date '11/11/2019')?.$methodName() } | Should -Throw -ErrorId 'Argument'

Aditya Patwardhan (@adityapatwardhan), your last commit had 20 failures in PowerShell-CI-static-analysis
(These are 5 of the failures)

Verify Markdown Links.Verify links in /home/vsts/work/1/s/README.md.https://docs.microsoft.com/powershell/scripting/setup/installing-powershell-core-on-windows?view=powershell-6 should work

retry of URL failed with error: Response status code does not indicate success: 404 (Not Found).
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

Verify Markdown Links.Verify links in /home/vsts/work/1/s/README.md.https://docs.microsoft.com/powershell/scripting/setup/installing-powershell-core-on-linux?view=powershell-6#ubuntu-1804 should work

retry of URL failed with error: Response status code does not indicate success: 404 (Not Found).
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

Verify Markdown Links.Verify links in /home/vsts/work/1/s/README.md.https://docs.microsoft.com/powershell/scripting/setup/installing-powershell-core-on-linux?view=powershell-6#ubuntu-1604 should work

retry of URL failed with error: Response status code does not indicate success: 404 (Not Found).
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

Verify Markdown Links.Verify links in /home/vsts/work/1/s/README.md.https://docs.microsoft.com/powershell/scripting/setup/installing-powershell-core-on-linux?view=powershell-6#debian-9 should work

retry of URL failed with error: Response status code does not indicate success: 404 (Not Found).
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

Verify Markdown Links.Verify links in /home/vsts/work/1/s/README.md.https://docs.microsoft.com/powershell/scripting/setup/installing-powershell-core-on-linux?view=powershell-6#centos-7 should work

retry of URL failed with error: Response status code does not indicate success: 404 (Not Found).
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

One open issue: [System.DBNull]::Value?.GetTypeCode() and [NullString]::Value?.GetType() will return nothing, which might raise confusion. We need to discuss and decide if it's fine to have this semantics for the null-conditional operator.
Talked with Aditya Patwardhan (@adityapatwardhan) offline, and we will discuss and address this in the RC release.
/cc James Truher (@JamesWTruher) Steve Lee (@SteveL-MSFT) Rob Holt (@rjmholt)

Filed issue: #11084

PoshChan-Bot (@PoshChan) please retry static

Aditya Patwardhan (@adityapatwardhan), successfully started retry of PowerShell-CI-static-analysis

Dongbo Wang (@daxian-dbw) Ready to merge?

🎉v7.0.0-preview.6 has been released which incorporates this pull request.:tada:

Handy links:

Release Notes

…age (PowerShell#10960)

Aditya Patwardhan (adityapatwardhan) requested review from Dongbo Wang (daxian-dbw) and Rob Holt (rjmholt) November 1, 2019 00:04

PoshChan-Bot (PoshChan) reviewed Nov 5, 2019

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