System.DayOfWeek does not contain op_Addition - powershell

Question

I have a method that returns last Saturday's Date, and it used to work on the old place I ran it, but I moved it to a new location to run it and it's not working. I'm not sure if this version of powerShell is different and that's the issue. It's saying PSVersion is 4 in the new location. The old location had PSVersion of 5.1.
This is my method, and when I check $newdate, it is empty after this runs and during run.
function GetLastSaturdayDate()
{
$date = Get-Date
$newdate = $date.AddDays(-($date.DayOfWeek+1)%7)
return $newdate
}
When I run the commands at the ps commandline, it says the following. I don't see this error message when I'm just running the script:
Method invocation failed because [System.DayOfWeek] does not contain a method named 'op_Addition'.
At line:1 char:1
+ $newda = $date.AddDays(-($date.DayOfWeek+1)%7)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (op_Addition:String) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound
Any ideas how to get date addition to work in the older powershell version? Maybe I need to include or use something like math?

Answer 1

Because your DayOfWeek member is an enumeration of type System.DayOfWeek, powershell is trying to use the System.Enum type to perform addition, but that type does not support addition unless it has a Flags attribute. The way to remediate this is by flipping your operands so the DayOfWeek gets coerced to System.Int32 instead:
1 + $date.DayOfWeek
Alternatively (for style), typecast it yourself:
[int]$date.DayOfWeek+1