Assigning the result of an addition (+ operator) with an IList LHS back to that LHS should preserve the list (collection) type #5805
Description
The following idioms should work generically with extensible collections that implement the IList interface and therefore have an .Add(Object) method.
# The following should both call $list.Add($newElement) behind the scenes:
$list = $list + $newElement
$list += $newElementThis would match the current array behavior (although a new array is created every time, given that arrays are fixed-size collections), as well as the behavior with hashtables (with hashtables as the RHS values too).
The current behavior is unexpected:
- with an unconstrained variable: quietly converts the LHS to an array:
$list = [System.Collections.ArrayList] (1, 2)
$list += 3 # !! Quietly converts the ArrayList to Object[]
$list.GetType().Name . # !! Object[] - with a type-constrained variable: creates a new instance
[System.Collections.ArrayList] $list = 1, 2 # type-constrained ArrayList
$orgList = $list # save reference to original list
$list += 3 # !! Quietly creates a *new instance*
[object]::ReferenceEquals($list, $orgList) # !! $FalseEnvironment data
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breaking change that may affect usersPS-Committee has reviewed this and made a decisionthe issue may not have a clear classification yet. The issue may generate an RFC or may be reclassifIssue has had no activity for 6 months or moreUp-for-grabs issues are not high priorities, and may be opportunities for external contributorscore PowerShell engine, interpreter, and runtime