Where methods (Clear, ForEach, Where, etc.) of powershell array are defined?

Question

According to the offical document about arrays in PowerShell, several methods are defined for arrays, for example Clear(), ForEach(), Where(), etc. Following code tested these methods:

$arr = 1..2
$arr.Clear()
$arr.Length

write "--------------------------------------------------"
$arr = 1..2
$arr.ForEach({$_ + 1})

write "--------------------------------------------------"
$arr = 65..90
$arr.Where({($_ % 2) -eq 0})

Output:

2
--------------------------------------------------
2
3
--------------------------------------------------
66
68
70
72
74
76
78
80
82
84
86
88
90

Fine! And, methods such as ForEach() have many overloads that are not tested here.

But where these methods are defined? I mean, What is the class that contains the definition of these methods? As far as I know, these methods are not defined in .net core. (I use PowerShell 7)

Answer 1

Clear() is part of the IList interface implemented by System.Array, which is the base type for collections (System.Object[]) in PowerShell.

To see all native methods available, use:

$arr.PSObject.Methods
# or
Get-Member -InputObject $arr -MemberType Methods

However: The Where() and ForEach() "magic" methods were introduced in v4 and are actually PowerShell-specific extension methods (as more performant alternatives to ForEach-Object and Where-Object), defined in System.Management.Automation.EnumerableOps. Have a look at the source:

internal static object Where(IEnumerator enumerator, ScriptBlock expressionSB, WhereOperatorSelectionMode selectionMode, int numberToReturn)

internal static object ForEach(IEnumerator enumerator, object expression, object[] arguments)

Answer 2

Why do you state As far as I know, these methods are not defined in .net core. (I use PowerShell 7)? Really:

$PSVersionTable.PSVersion | Out-Default
$arr = 1..2
$arr.GetType() | Get-Member -MemberType Methods -Static

Major  Minor  Patch  PreReleaseLabel BuildLabel
-----  -----  -----  --------------- ----------
7      0      3


   TypeName: System.Object[]

Name            MemberType Definition
----            ---------- ----------
AsReadOnly      Method     static System.Collections.ObjectModel.ReadOnlyCollection[T] …
BinarySearch    Method     static int BinarySearch[T](T[] array, int index, int length,…
Clear           Method     static void Clear(array array, int index, int length)
ConstrainedCopy Method     static void ConstrainedCopy(array sourceArray, int sourceInd…
ConvertAll      Method     static TOutput[] ConvertAll[TInput, TOutput](TInput[] array,…
Copy            Method     static void Copy(array sourceArray, array destinationArray, …
CreateInstance  Method     static array CreateInstance(type elementType, int length), s…
Empty           Method     static T[] Empty[T]()
Equals          Method     static bool Equals(System.Object objA, System.Object objB)
Exists          Method     static bool Exists[T](T[] array, System.Predicate[T] match)
Fill            Method     static void Fill[T](T[] array, T value), static void Fill[T]…
Find            Method     static T Find[T](T[] array, System.Predicate[T] match)
FindAll         Method     static T[] FindAll[T](T[] array, System.Predicate[T] match)
FindIndex       Method     static int FindIndex[T](T[] array, System.Predicate[T] match…
FindLast        Method     static T FindLast[T](T[] array, System.Predicate[T] match)
FindLastIndex   Method     static int FindLastIndex[T](T[] array, System.Predicate[T] m…
ForEach         Method     static void ForEach[T](T[] array, System.Action[T] action)
IndexOf         Method     static int IndexOf(array array, System.Object value), static…
LastIndexOf     Method     static int LastIndexOf(array array, System.Object value), st…
new             Method     System.Object[] new(int )
ReferenceEquals Method     static bool ReferenceEquals(System.Object objA, System.Objec…
Resize          Method     static void Resize[T]([ref] T[] array, int newSize)
Reverse         Method     static void Reverse(array array), static void Reverse(array …
Sort            Method     static void Sort(array array), static void Sort(array keys, …
TrueForAll      Method     static bool TrueForAll[T](T[] array, System.Predicate[T] mat…