PowerShell type name evaluation

Question

Unfortunately Powershell ISE can't show intellisense for .NET Classes Constructor. I have found a script which can get the list of Constructor:

[System.IO.StreamWriter].GetConstructors() |
 ForEach-Object {
    ($_.GetParameters() |
        ForEach-Object {
            ‘{0} {1}’ -f $_.Name, $_.ParameterType.FullName 
        }) -join ‘,’
 }

It works perfectly

Is there a way to use a variable instead of a fixed class name ? Somethink like that:

Param(
    [Parameter(Mandatory=$True)]
    [string]$class 
)

[$class].GetConstructors() |
 ForEach-Object {
    ($_.GetParameters() |
        ForEach-Object {
            ‘{0} {1}’ -f $_.Name, $_.ParameterType.FullName 
        }) -join ‘,’
 } 

I will call the Script in this way:

Script.ps1 System.IO.StreamWriter

Now it return the following error:

At D:\LAB\POWERSHELL\CMD-LETS\GetConstructor.ps1:6 char:2 + [$class].GetConstructors() | + ~ Missing type name after '['. At D:\LAB\POWERSHELL\CMD-LETS\GetConstructor.ps1:6 char:26 + [$class].GetConstructors() | + ~ An expression was expected after '('. + CategoryInfo : ParserError: (:) [], ParseException + FullyQualifiedErrorId : MissingTypename

Answer 1

You'll need to create a Type object from the $Class string argument:

$script = {
Param(
    [Parameter(Mandatory=$True)]
    [string]$class
)

([Type]$Class).GetConstructors() |
 ForEach-Object {
    ($_.GetParameters() |
        ForEach-Object {
            ‘{0} {1}’ -f $_.Name, $_.ParameterType.FullName 
        }) -join ‘,’
 }
 }

 &$script 'system.io.streamwriter'

stream System.IO.Stream
stream System.IO.Stream,encoding System.Text.Encoding
stream System.IO.Stream,encoding System.Text.Encoding,bufferSize System.Int32
stream System.IO.Stream,encoding System.Text.Encoding,bufferSize System.Int32,leaveOpen System.Boolean
path System.String
path System.String,append System.Boolean
path System.String,append System.Boolean,encoding System.Text.Encoding
path System.String,append System.Boolean,encoding System.Text.Encoding,bufferSize System.Int32