Compound-assignment-operators

Compound assignment operators

Differences between PowerShell v2 and v3

From WMF 3 Release Notes.docx at WMF 3.0:

Change

Read/Modify/Write operators no longer use dynamic scoping for the Read
operation. Also, compound equality operators (including +=, -=, *=, %=, ++,
--) do not use dynamic scoping.  The variable is always in the current scope.

Sample

$x = 1
& { $x += 1; $x }
# Returns 2 in Windows PowerShell 2.0
# Returns 1 in Windows PowerShell 3.0

Error Message

No error. Results differ.

Workaround

Rewrite to use only the simple assignment operator:
$x = 1
& { $x = $x + 1; $x}

Scripts

• Test-1.1.ps1 shows different results in v2 and v3 for the operator +=.
• Test-1.2.ps1 shows same results in v2 and v3 for the operator ++, in contrast to the release notes.

In PowerShell v3+ results may be affected by other commands

The script Test-2.ps1 in v3+ shows how the result of the operator += is affected by the seemingly unrelated preceding New-Variable added to the script Test-1.1.ps1.

---

• Stack Overflow question
• Microsoft Connect 1341920