Setting property values with the .ForEach() array method doesn't work with a single [pscustomobject] instance.

[mklement0]

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Steps to reproduce

.ForEach() has an overload that allows setting property values by name and (array of) property values.

This works in general, but unexpectedly not with a single [pscustomobject] instance (as later discovered, it does work with arrays of [pscustomobject] instances).

($obj = [pscustomobject] @{ p = 1 }).ForEach('p', 42)

Expected behavior

No output, and $obj.p should report 42 afterwards.

Actual behavior

1 - the current property value - is output, and the attempt to assign a new value is ignored.

Error details

No response

Environment data

PowerShell Core 7.3.0-preview.1

Visuals

No response

[scriptingstudio]

strange, with single brackets does not work but double do

@(($obj = [pscustomobject] @{ p = 1 })).ForEach('p', 42)
$obj

 p
 -
42

[mklement0]

@scriptingstudio, good find; it's the use of @(....) that makes the difference here - the inner (...) are only needed in order to pass the value of the $obj assignment through.

In other words: it's only when calling .ForEach() on a scalar [pscustomobject] instance that the bug surfaces.
It works fine on an array of [pscustomobject] instances.

[jhoneill]

I thought .foreach() and .where() were for arrays only. Documentation of the .foreach() method is pretty thin - it's not mentioned in About_foreach for example. It certainly does work for some scalars as described above (so I was wrong :-) ) , but I wonder if it has a low profile because has never reliably implemented some features ? Maybe I'm just not finding the right search terms, but I can't find any examples of that syntax in use...

[scriptingstudio]

@jhoneill just a couple of doc examples https://mcpmag.com/articles/2015/12/02/where-method-in-powershell.aspx, https://powershellmagazine.com/2014/10/22/foreach-and-where-magic-methods

Microsoft Certified Professional Magazine Online

Introduction to the Where Method in PowerShell -- Microsoft Certified Professional Magazine Online

This feature, new to version 4 of PowerShell, will be a tool you use every day.

ForEach and Where magic methods

ForEach and Where are two frequently used concepts that have been available in PowerShell since version 1 came out in 2006.

[iSazonov]

I thought .foreach() and .where() were for arrays only.

Yes, but Count works for scalar and foreach()/where() too.

[mklement0]

They're (now) documented in about_Arrays and briefly mentioned in about_Intrinsic_Members

In the former topic they're under the heading "Methods of Arrays", so I've been calling them array methods on Stack Overflow for a while.

Yes, they work on scalars too - as they should, given PowerShell's unified handling of scalars and collections (just like you can send a scalar as-is through the pipeline):

(1).ForEach({ $_ })  # -> 1
(1).Where({ $true }) # -> 1

(What makes for a slightly awkward asymmetry, however, is that - unlike in the pipeline - the return value is always a collection, namely of type [System.Collections.ObjectModel.Collection[PSObject]])

[SeeminglyScience]

Looks like the binder is calling InvokeAdaptedMember instead of EnumerableOps.ForEach.

Here's the Bind result for a scalar int:

if (((target is int) && (_version == 0)) && ((member is string) && (value is string)))
{
    return EnumerableOps.ForEach(
        Fake.Dynamic<Func<CallSite, IEnumerator, IEnumerator>>(PSEnumerableBinder.Get())(
            Fake.Dynamic<Func<CallSite, object[], IEnumerator>>(PSEnumerableBinder.Get())(
                new object[] { target })),
        member,
        new object[] { value });
}

(side note, dunno what's up with the double enumerate there)

And here it is for a pscustomobject:

if ((((_version == 0) && (target is PSObject)) && ((PSObject.Base(target) == target) && (member is string))) &&
    (value is string))
{
    return PSInvokeMemberBinder.InvokeAdaptedMember(PSObject.Base(target), "ForEach", new object[] { member, value });
}

[jhoneill]

@scriptingstudio

@jhoneill just a couple of doc examples

Yes I'd found Boe Prox's one which basically says "this is not for scalars", and Kirk's one says ", two new “magic” methods were introduced for collection types" So not scalars either. These are community experts explaining it, not information from the authors.

I thought .foreach() and .where() were for arrays only.

Yes, but Count works for scalar and foreach()/where() too.

Yes, @iSazonov I've relied on that for years... I use .where() heavily and I'm now thinking "Do I only use it on what I know will be an array, or do I trust it to do the right thing with a scalar."

The syntax Mike's using is in about_arrays (not About_foreach) and there is a note in about_Intrinsic_Members

There are certainly some things that are not right ...

ps > $s = "one two three"
ps > $s.where({$_.length -gt 10 } )
one two three

ps > $s.where({$_.length -gt 10 } ) += "four"
InvalidArgument: Cannot convert value "one two three" to type "System.Management.Automation.WhereOperatorSelectionMode".  Error: "Unable to match the identifier name one two three to a valid enumerator name. Specify one of the following enumerator names and try again:
Default, First, Last, SkipUntil, Until, Split"

ps > > $s.where({$_.length -gt 10 } ) + "four"
one two three
four

The second has turned the scalar into an array. But the first one seems have turned the whole thing inside out.

[SeeminglyScience]

Aside from the second one (which appears to be a very bizarre but separate binding bug) that all looks right. Where and ForEach always return a Collection<> regardless of the input.

[ghost]

🎉This issue was addressed in #17213, which has now been successfully released as v7.3.0-preview.4.:tada:

Handy links:

• Release Notes