Let's take the classic first-order functions example:
function Get-MyName { "George" }
function Say-Hi([scriptblock]$to) {
Write-Host ("Hi "+(& $to))
}
This works just fine:
Say-Hi { "Fred Flintstone" }
this does not:
Say-Hi Get-MyName
because Get-MyName is evaluated, not passed as a value itself. How do I pass Get-MyName as a value?
You have to pass Get-Myname as a scriptblock, because that's how you've defined the variable type.
Say-Hi ${function:Get-MyName}
Say-Hi {Get-MyName}? Is there a type other than [scriptblock] that would allow passing of named functions?
Get-MyName took parameters, in your version you would have to know all the parameters that it is invoked with and forward them manually, if you're passing the function directly (as you would in js or c#) its parameters are whatever it is invoked with from inside Say-HiIf you are ready to sacrifice the [scriptblock] parameter type declaration
then there is one more way, arguably the simplest to use and effective. Just
remove [scriptblock] from the parameter (or replace it with [object]):
function Get-MyName { "George" }
function Say-Hi($to) {
Write-Host ("Hi "+(& $to))
}
Say-Hi Get-MyName
Say-Hi { "George" }
So now $to can be a script block or a command name (not just a function but also alias, cmdlet, and script).
The only disadvantage is that the declaration of Say-Hi is not so self describing.
And, of course, if you do not own the code and cannot change it then this is
not applicable at all.
I wish PowerShell has a special type for this, see this suggestion.
In that case function Say-Hi([command]$to) would be ideal.
This might be a better example to illustrate the question, and details of execution scope. @mjolinor's answer appears to work nicely for this use case:
function Get-MyName($name) { $name; throw "Meh" }
function Say-Hi([scriptblock]$to) {
try {
Write-Host ("Hi "+(& $to $args)) # pass all other args to scriptblock
} catch {
Write-Host "Well hello, $_ exception!"
}
}
The command and its output:
PS C:\> Say-Hi ${function:Get-MyName} 'George'
Well hello, Meh exception
In particular, I'm using this pattern for wrapping functions that work with a flaky remote SQL Server database connection, which sleep, then retry several times before finally succeeding or throwing a higher exception.
Strictly based on your code, the correct answer is this:
Say-Hi {(Get-MyName)}
This will produce "Hi George"
Get-MyName is called. In mjolinor's example there is a direct reference to the Get-MyName-function passed. (With parameters this variation could be written like Say-Hi { Get-MyName @args } whereas mjolinor's would work without modification.)