What is the right way to check a switch parameter - powershell

Question

What is the right way to check value of a switch?
function testSwitch
{
Param(
[switch] $swth
)
Write-Host "Value of swth is $swth"
if($swth.IsPresent){
Write-host "Switch is present"
}
if($swth){
Write-Host "Switch is present"
}
}
testSwitch -swth
I know both if statement works fine, but how?

Answer 1

$swth.IsPresent and $swth can be used interchangeably, because in a Boolean context (such as an if conditional) $swth (an instance of type [switch] representing a switch parameter) effectively returns the value of the .IsPresent property.[1]
In fact, $swth is probably preferable[2], not just for concision, but because the .IsPresent property is somewhat confusingly named:
.IsPresent doesn't indicate the presence of the switch per se, but whether its value is $true.
While specifying a switch by itself - -swth - implies both, the same isn't true if you explicitly set it to $false: Passing -swth:$false makes .IsPresent return $false, even though the switch is clearly present.
Passing $false explicitly isn't common, but has its uses, such as when opting out of a confirmation prompt with -Confirm:$false, and when programmatically constructing arguments.
Therefore, if you want to distinguish between the user not passing the switch and the user passing it with value $false, .IsPresent won't help you - you'll have to use $PSBoundParameters.ContainsKey('swth')
[1] On conversion to Boolean, which happens in method LanguagePrimitives.IsTrue(), PowerShell calls a [switch] instance's .ToBool() method, which in turn returns the private backing variable behind the .IsPresent property.
[2] The only caveat is that you must be aware that $swth is not a Boolean ([bool]), but of type [switch], which may matter in other contexts.

Answer 2

It would be more simple to just use an if/else clause:
Function Get-FruitDetails {
[CmdLetBinding()]
Param (
[String]$Fruit,
[Switch]$Yellow
)
Write-Verbose "Get fruit details of $Fruit"
$Result = [PSCustomObject]#{
Fruit = $Fruit
Yellow = $null
}
if ($Yellow) {
Write-Verbose 'Color is yellow'
$Result.Yellow = $true
}
else {
Write-Verbose 'Color is not yellow'
$Result.Yellow = $false
}
$Result
}
Get-FruitDetails -Fruit 'Banana' -Yellow -Verbose
Get-FruitDetails -Fruit 'Kiwi' -Verbose
This will output the following:
Fruit Yellow
----- ------
Banana True
Kiwi False
Some tips:
Avoid using Write-Host, it's meant for console programs. You're better of using Write-Verbose and adding the -Verbose switch if you want to see the messages
Try to use PowerShell approved verbs for function names. These can be easily found using Get-Verb. It will make it easier for others to see what your function does Get, Set, Remove, ...