Consider this example, a ps1 script test.ps1

function MyTestFunction
{
    [CmdletBinding()]
    param ()

    try
    {
        [bool]$functionBool= $null
    }
    catch {throw $_}

    Get-Variable 'functionBool'
}

MyTestFunction -ErrorAction Stop

[bool]$scriptBool= $null

• There are 2x illegal variable declarations in the above example (System.Boolean is a non-nullable type).

Resulting output when this .ps1 script is run by:

• Dot-sourcing . the script

  Name                           Value
  ----                           -----
  functionBool                   False
  Cannot convert value "" to type "System.Boolean". Boolean parameters accept only Boolean values and numbers, such as $True, $False, 1 or 0.
  At C:\scripts\test.ps1:17 char:1
  + [bool]$scriptBool = $null
  + ~~~~~~~~~~~~~~~~~~~~~~~~~
      + CategoryInfo          : MetadataError: (:) [], ArgumentTransformationMetadataException
      + FullyQualifiedErrorId : RuntimeException
  

  • $functionBool is transformed to $false
    • No exception is thrown
  • $scriptBool is not transformed
    • An (expected) ArgumentTransformationMetadataException exception is thrown

• Using the call operator &

  Name                           Value
  ----                           -----
  functionBool                   False
  

  • No exception is thrown at all, for either operation.

• As expected, doing the same operation in the global scope in the CLI throws an exception:

  PS C:\> [bool]$scriptBool = $null
  
  Cannot convert value "" to type "System.Boolean". Boolean parameters accept only Boolean values and
  numbers, such as $True, $False, 1 or 0.
  At line:1 char:1
  + [bool]$scriptBool = $null
  + ~~~~~~~~~~~~~~~~~~~~~~~~~
      + CategoryInfo          : MetadataError: (:) [], ArgumentTransformationMetadataException
      + FullyQualifiedErrorId : RuntimeException
  

Questions

• What am I not understanding about scopes and PowerShell's behavior in regards to type coercion, specifically the example mentioned at the top?
  • In other words, why doesn't the line [bool]$functionBool= $null throw an exception?
• If I set a breakpoint on line #8 (where [bool]$functionBool= $null is declared) in VS Code/ISE and step through, program flow will end up in the catch block of the MyTestFunction function.
  • Confusingly, removing the breakpoint produces a different result where the catch{} block is not executed.