Comma Before Parentheses in Variable Assignment

Question

I'm using the S.DS.P PowerShell module in a PowerShell script of mine. In it, I have to create the following object:

$ADUserEntry = @{"distinguishedName"=$null;"objectClass"=$null;"sAMAccountName"=$null;"unicodePwd"=$null;"userAccountControl"=0};

In the documentation of the module, it's stated that I have to do the following assignment to the unicodePwd field of a variable created using this object:

$obj.unicodePwd = ,([System.Text.Encoding]::Unicode.GetBytes("$randomPassword") -as [byte[]]);

Notice how there's a comma before the first parentheses. What is that comma doing there?

Answer 1

As Lee_Dailey has pointed out, what you're seeing is the unary form of the (unfortunately named) "comma operator", i.e., PowerShell's array-construction operator.

The unary form creates a single-element array that wraps its (one and only) operand; the array's type is [object[]], as usual in PowerShell:

$arr = , 'foo'  # wrap string 'foo' in a single-element array
$arr.GetType().Name # the array's type -> 'Object[]'
$arr[0].GetType().Name # the type of the array's one and only element -> 'String'

Note that while you can even wrap arrays that way, PowerShell's operator-precedence rules require a literal array operand to be enclosed in (...):

# OK - wraps array 1, 2 in a single-element array.
$arr = , (1, 2) 

# !! DOES SOMETHING DIFFERENT:
# Creates a 2-element array whose 1st element is integer 1 wrapped in a
# single-element array
$arr = , 1, 2

The binary form constructs an array from the operands, as expected:

$arr = 1, 2, 3  # 3-element array whose elements are integers 1 and 2 and 3

---

As an aside, re the specific command shown:

,([System.Text.Encoding]::Unicode.GetBytes("$randomPassword") -as [byte[]])

Neither , nor -as [byte[]] are needed in this scenario, because [System.Text.Encoding]::Unicode.GetBytes() directly returns a [byte[]] array.