Flex/ActionScript3: keyword "with" hides misspelled property names

Question

In Flex 3,

var anInstance : MyClass = new MyClass();
with (anInstance)
{
    property1 = "fred";
    property2 = 5;
    propert3 = 7;
}

does NOT flag "propert" as a non-existent property name. I thought this was a remainder of the evil JavaScript object behavior (referring to a property name of an object implicitly creates it), but it seems to be a side-effect of the "with".

This makes me very sad as the "with" was a little reminder of Delphi (except it works correctly there).

Am I missing something here?

Answer 1

From reading the documentation:

Actionscript apparently bubbles out for scope resolution on embedded variables (not surprising, since the syntax doesn't require an explicit dereference symbol like "." or "->" to indicate which variable names should be "withed".) So you effectively are creating a variable at global scope named propert3.

---

EDIT after thinking about why this "problem" exists -

Javascript is the epitome of non-strict typing. And Actionscript, being a strict superset of Javascript, can't enforce strict typing except as declared by its own extensions to the language - which means it must support untyped variables.

Answer 2

Some classes are dynamic (e.g. movieclip) and can have properties added to them at runtime:

http://flexblog.faratasystems.com/?p=95