Parameter set cannot be resolved

Question

function f {
  param(
    [Parameter(ParameterSetName='A', Position=0)]
    [int] $Num,
    [Parameter(ParameterSetName='A', Position=1)]
    [Parameter(ParameterSetName='B', Position=0)]
    [scriptblock] $Script
  )
}

f 123 {}
f {}

Why can't the parameter set of the second call be resolved? It seems perfectly resolvable. At least there seems to be enough information for that.

Answer 1

You would need to add a DefaultParameterSetName to avoid ambiguity. On the second function call, PowerShell can't tell if you're wanting to use the parameter set A or B.

function f {
    [CmdletBinding(DefaultParameterSetName = 'B')]
    param(
        [Parameter(ParameterSetName = 'A', Position = 0)]
        [int] $Num,

        [Parameter(ParameterSetName = 'A', Position = 1)]
        [Parameter(ParameterSetName = 'B', Position = 0)]
        [scriptblock] $Script
    )

    $PSCmdlet.ParameterSetName
}

f 123    # A
f 123 {} # A
f {}     # B