optional variables - VB.NET := Operator

Question

What does the following mean?

Class.Function(variable := 1 + 1)

What is this operator called, and what does it do?

Answer 1

It is used to assign optional variables, without assigning the previous ones.

sub test(optional a as string = "", optional b as string = "")
   msgbox(a & b)
end sub

you can now do

test(b:= "blaat")
'in stead of
test("", "blaat")