Passing enum values to a function in PowerShell

It's a little bit unexpected - you need to wrap it in parenthesis so that the value is evaluated:

> IsItFriday ([System.DayOfWeek]::Monday)

also it is possible to pass only strings like this:

> IsItFriday Mondayno> IsItFriday Fridayyes

PowerShell will convert it to the enum type. Handy, isn't it :)

To avoid the error put the enum value in parenthesis:

PS > IsItFriday ([System.DayOfWeek]::Monday)  noPS > IsItFriday ([System.DayOfWeek]::Friday)  yes

Yes, that is a rather confusing error message. I think you would understand better with an example:

Get-ChildItem -Path C:\

Notice there are no quotes around C:\ because, one, it implcitly gets converted to a string, and two, it is not necessary to enclose a path which does not contain spaces when you pass the path as a parameter to some callee.

So lets go back to your function, and change it slightly:

function IsItFriday($dayOfWeek) {    $dayOfWeek.GetType()    if ($dayOfWeek -eq [System.DayOfWeek]::Friday)     {        "yes"    }     else     {        "no"    }}IsItFriday [System.DayOkWeek]::Monday

...and the output:

IsPublic IsSerial Name                                     BaseType                                                                                        -------- -------- ----                                     --------                                                                                        True     True     String                                   System.Object                                                                                   no

See what happened there? PowerShell thinks you are passing in a string instead of an enumeration value, so that's why you get Cannot convert value "[System.DayOfWeek]::Monday" because that is the literal string that gets passed in.