Powershell splatting a nested hash table - powershell

Question

I have a function that returns a complex nested hash table data structure, where part of it forms the arguments for a further function call, and part of it is strings for reporting errors that result in the arguments not being populated.
Ideally I would like to splat just the arguments hash table, but I am starting to think that can't be done.
So, an example of the basic problem looks like this...
function Test {
param (
[String]$A,
[String]$B,
[String]$C
)
Write-Host "A: $A"
Write-Host "B: $B"
Write-Host "C: $C"
}
$data = #{
arguments = #{
A = 'A string'
B = 'Another string'
C = 'The last string'
}
kruft = 'A string that doesn not need to get passed'
}
Ideally I want to splat $data.arguments, so something like this...
Test #data.arguments
But that doesn't work, resulting in the error
The splatting operator '#' cannot be used to reference variables in an expression. '#data' can be used only as an argument to a command. To
reference variables in an expression use '$data'.
So I tried...
Test #(data.arguments)
Which results in the error
data.arguments : The term 'data.arguments' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the
spelling of the name, or if a path was included, verify that the path is correct and try again.
I also tried...
Test #($data.arguments)
Which results in the whole hash table being passed as a single argument and the output is
A: System.Collections.Hashtable
B:
C:
What DOES work is...
$arguments = $data.arguments
Test #arguments
Which has me thinking you really cannot splat anything but a simple variable that is an appropriate hash table. But, I am hoping someone can verify that is indeed true, or point out the solution I haven't come up with yet.
The actual code requires 5 arguments, with somewhat verbose names because I prefer descriptive names, so splatting is very much an appropriate solution. Needing to make a new variable with just the hash table to be passed isn't an issue, just wondering if it really is the only option.

Answer 1

That's not possible.
Any variable (and only variables) provided with "#" instead of "$" for a function parameter is declared as TokenKind "SplattedVariable".
See:
https://learn.microsoft.com/en-us/dotnet/api/system.management.automation.language.tokenkind?view=powershellsdk-7.0.0
PS:
Some quick tests from my side which could have succeed (apart from PS design):
Write-Host 'Test 1' -ForegroundColor Yellow
Test #$data.arguments
Write-Host 'Test 2' -ForegroundColor Yellow
Test #$($bla = $data.arguments)
Write-Host 'Test 3' -ForegroundColor Yellow
Test #$bla = $data.arguments
Write-Host 'Test 4' -ForegroundColor Yellow
Test #$bla = $data.arguments.GetEnumerator()
Write-Host 'Test 5' -ForegroundColor Yellow
Test #$($data.arguments.GetEnumerator())
... but they didn't.

Answer 2

I cannot claim to fully understand what you're attempting, but here are a couple of solutions that might help.
Your Test function is expecting three strings, but I don't see anything in your example that satisfies that. I would either change it to accept a Hashtable (which is the data type in question) or have it accept a string array and pass $data.arguments.values
Using a Hashtable:
function Test {
param (
[Hashtable]$hash
)
write-host $hash.A
write-host $hash.B
write-host $hash.C
}
Test $data.arguments
Using a String array:
function Test {
param (
[String[]]$a
)
$a | % { write-host $_ }
}
Test $data.arguments.values

Answer 3

This is a totally artificial way (more of a hack) of doing this but you could pass it as a hash table then self-call with the arguments splatted
function Test {
param (
[Parameter()]
[hashtable]$ht,
[String]$A,
[String]$B,
[String]$C
)
if($null -eq $ht){
Write-Host "A: $a"
Write-Host "B: $B"
Write-Host "C: $C"
}
else
{
Write-Host "ht.A: $($ht.a)"
Test -a $($ht.A+ " new blob") -b $ht.B -c $ht.C
Test #ht
}
}
$tdata = #{
arguments = #{
A = 'A string'
B = 'Another string'
C = 'The last string'
}
kruft = 'A string that doesn not need to get passed'
}
Write-Host 'Test ht' -ForegroundColor Yellow
Test -ht $tdata.arguments