The testit() method is a closure. aString has fallen out of scope but testit() can still execute on it. testit2() is using a variable that hasn’t fallen out of scope (mystring) but which was also not been passed into testit2(). Is testit2() considered a closure?
string mystring = 'hello world'; Action testit = new Action(delegate { string aString = 'in anon method'; Debug.WriteLine(aString); }); testit(); //capture mystring. Is this still a closure? Action testit2 = new Action(delegate { Debug.WriteLine(mystring); }); //mystring is still in scope testit2(); In the second example, mystring can be updated outside of the method and those changes will be reflected in testit2(). This doesn’t behave like a normal method, which would only be able to capture mystring as a parameter.
Both examples are anonymous functions. The second of which use a closure in order to capture the local variables. The scope lifetime of the variable with respect to the anonymous function does not affect whether or not a closure is created to use it. As long as the variable is defined outside a anonymous function and used within, a closure will be created.
The first anonymous function uses no local state, therefore does not need a closure. It should compile down to a static method.
This is necessary because the anonymous function can live past the lifetime of the current function. Therefore all locals used in a anonymous function must be captured in order to execute the delegate at a later time.