Hashtables: Use previous property to generate next property

Question

Is there a way to generate a Hashtable that uses properties just defined in the hashtable to create the next property down the line? I know I can just do it line by line instead, but I would like to maintain the formatting I currently have as I like how it reads.

$RequestedSpace = @{}
$RequestedSpace.Clear()
$RequestedSpace = @{
    Gb = (Read-Host "How much space (in Gb) would you like left over?")
    b = $RequestedSpace.Gb * 1Gb
};
$RequestedSpace.Gb
$RequestedSpace.b

The above results in a null value for $RequestedSpace.b

The below works, but is significantly uglier IMO

$RequestedSpace = @{}
$RequestedSpace.Clear()
$RequestedSpace.Gb = Read-Host "How much space (in Gb) would you like left over?"
$RequestedSpace.b = [bigint]$RequestedSpace.Gb * 1gb

Answer 1

You can take advantage of the fact that:

• you can define an auxiliary variable and use the assignment as an expression by enclosing it in (...), the grouping operator, which passes the assigned value through

• entries are defined in sequence, so subsequent entries can refer to aux. variables defined earlier.

@{
  # Note the *definition* of aux. variable $gb
  Gb = ($gb = [double] (Read-Host "How much space (in Gb) would you like left over?"))
  # Note the *use* of $gb
  b = $gb * 1Gb
}

Assuming you enter 2 when prompted, you'l get the following display output:

Name                           Value
----                           -----
Gb                             2
b                              2147483648

---

Note:

• The technique works for hashtable literals, as shown above (@{ ... }), as well as [pscustomobject] literals ([pscustomobject] @{ ... }).

• GitHub suggestion #13782 looks for a built-in way to allow hashtable entries to reference one another.