Peter Hinchley

Learning in Public

✪ Object-Oriented PowerShell without PowerShell 5.0

PowerShell 5.0 introduces support for object-oriented programming, however, we don't always have the luxury of working on systems where PowerShell 5.0 is installed. When I am stuck using an older version of PowerShell, and I feel the need to write object-oriented code, I use the following approach:

function builder() {
  $instance = new-object psobject

  $instance | add-member -membertype scriptmethod -name property -value {
    param($name, $value)
    $this | add-member -membertype noteproperty -name $name -value $value -force
  }

  $instance | add-member -membertype scriptmethod -name method -value {
    param($name, $block)
    $this | add-member -membertype scriptmethod -name $name -value $block -force
  }

  return $instance
}

function person {
  param($name)

  $obj = builder

  $obj.property("name", $name)

  $obj.method("greet", {
    param($message)
    return "{0} {1}." -f $message, $this.name
  })

  return $obj
}

$pete = person "Pete"
$sara = person "Sara"

$pete.greet("Hi")
$sara.greet("Hello")

The output of the code is:

Hi Pete.
Hello Sara.

Even inheritance is simple:

function boy {
  param($name)

  $obj = person $name
  $obj.property("gender", 'male')
  return $obj
}

$fred = boy "Fred"
$fred.gender

The output is:

male