PowerShell: Cannot have local variables scoped inside a class method?

user_14222243 0
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I expect that inside a class method, I can have "local" variable scoped inside of the method, but it is not the case. The following is the test code:

class test_scope {
  $var = "class var"

  test_scope() {
  }

  [void] my_method() {
    $var = "method var"
  }
}

$obj = [test_scope]::new()
$obj.my_method()

I got an error message:

Line |
   8 |      $var = "method var"
     |      ~~~~
     | Cannot assign property, use '$this.var'.

This is surprising. How can I have local variables?

As a comparison, function (outside of a class, that is) can have local variables with the same name as the script variable. The following is an example:

$var2="global var"
function my_function() {
  $var2="function var"
  write-host $var2
  write-host $script:var2
}
my_function($null)

and I got the answer I expected:

function var
global var

As another comparison with Python:

class test_scope:
  var = "class var"

  def my_method(self):
    var = "method var"
    print(self.var)
    print(var)

obj = test_scope()
obj.my_method()

It works as expected:

function var
global var

so PowerShell is out of norm?

PS: I tested under PowerShell 5.0 and 7.0.

powershell-7.0 powershell-5.0 powershell oop
1 Answers

This is surprising. How can I have local variables?

You can have all the local variables you want in a class method - as long as their names don't collide with any class member name:

class MyClass
{
  [string]$var

  MyMethod()
  {
    $somethingOtherThanVar = "this should work"
  }
}

The reason PowerShell throws the error is a deliberate effort to be helpful - a class author who's new to the language or the class definition feature might assign to $var in a method, thinking that the $this.var (declared as $var outside the method body) would reflect the assignment and be in for a nasty surprise.

user_7126490
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