Parameters with default value not in PsBoundParameters? - function

Question

General code
Consider this code:
PS> function Test { param($p='default value') $PsBoundParameters }
PS> Test 'some value'
Key Value
--- -----
p some value
PS> Test
# nothing
I would expect that $PsBoundParameters would contain record for $p variable on both cases. Is that correct behaviour?
Question
I'd like to use splatting that would work like this for a lot of functions:
function SomeFuncWithManyRequiredParams {
param(
[Parameter(Mandatory=$true)][string]$p1,
[Parameter(Mandatory=$true)][string]$p2,
[Parameter(Mandatory=$true)][string]$p3,
...other parameters
)
...
}
function SimplifiedFuncWithDefaultValues {
param(
[Parameter(Mandatory=$false)][string]$p1='default for p1',
[Parameter(Mandatory=$false)][string]$p2='default for p2',
[Parameter(Mandatory=$false)][string]$p3='default for p3',
...other parameters
)
SomeFuncWithManyRequiredParams #PsBoundParameters
}
I don't want to call SomeFuncWithManyRequiredParams with all the params enumerated:
SomeFuncWithManyRequiredParams -p1 $p1 -p2 $p2 -p3 $p3 ...
Is it possible?

Answer 1

I know this question is very old, but I had a need for something like this recently (wanted to do splatting with a lot of default parameters). I came up with this and it worked very well:
$params = #{}
foreach($h in $MyInvocation.MyCommand.Parameters.GetEnumerator()) {
try {
$key = $h.Key
$val = Get-Variable -Name $key -ErrorAction Stop | Select-Object -ExpandProperty Value -ErrorAction Stop
if (([String]::IsNullOrEmpty($val) -and (!$PSBoundParameters.ContainsKey($key)))) {
throw "A blank value that wasn't supplied by the user."
}
Write-Verbose "$key => '$val'"
$params[$key] = $val
} catch {}
}
Shameless plug ahead: I decided to turn this into a blog post which has more explanation and a sample usage script.

Answer 2

It depends on how you define "bound" I guess i.e. is the value bound from a user supplied value or a default value supplied by the function? Honestly, it doesn't surprise me that it behaves the way it does as I view "bound" to mean the former - bound from user input. Anyway, you can solve this by patching the $PSBoundParameters variable e.g.:
function SimplifiedFuncWithDefaultValues {
param(
[Parameter(Mandatory=$false)][string]$p1='default for p1',
[Parameter(Mandatory=$false)][string]$p2='default for p2',
[Parameter(Mandatory=$false)][string]$p3='default for p3',
...other parameters
)
if (!$PSBoundParameters.ContainsKey(p1))
{
$PSBoundParameters.p1 = 'default for p1'
}
# rinse and repeat for other default parameters.
SomeFuncWithManyRequiredParams #PSBoundParameters
}

Answer 3

This is what I like to do:
foreach($localP in $MyInvocation.MyCommand.Parameters.Keys)
{
if(!$PSBoundParameters.ContainsKey($localP))
{
$PSBoundParameters.Add($localP, (Get-Variable -Name $localP -ValueOnly))
}
}

Answer 4

You could use a helper function similar to the Add-Variable function below:
function SimplifiedFuncWithDefaultValues {
param(
[Parameter(Mandatory=$false)][string]$p1='default for p1',
[Parameter(Mandatory=$false)][string]$p2='default for p2',
[Parameter(Mandatory=$false)][string]$p3='default for p3',
...other parameters
)
$PSBoundParameters | Add-Variable p1, p2, p3
SomeFuncWithManyRequiredParams #PSBoundParameters
}
function Add-Variable {
param(
[Parameter(Position = 0)]
[AllowEmptyCollection()]
[string[]] $Name = #(),
[Parameter(Position = 1, ValueFromPipeline, Mandatory)]
$InputObject
)
$Name |
? {-not $InputObject.ContainsKey($_)} |
% {$InputObject.Add($_, (gv $_ -Scope 1 -ValueOnly))}
}