Setting data type of an object at run time

Question

This is something of an advanced problem, so I hope there's
someone out there who can speak to this. I apologize for the length
of the post, I'm just trying to be clear about a rather unclear
conundrum. --
We all use arrays to hold collections of things. As you know,
an array is its self a type (Array) and so there is no way to
declare, for instance, an array of MovieClips or an array of
Strings. Heres what happens: lets pretend that we have 3 movie
clips clip1_mc, clip2_mc, and clip3_mc, and an Array called
anArray. so we can legally do this. anArray.push( clip1_mc );
anArray.push( clip2_mc ); anArray.push( clip3_mc );. An array of
size 3. Now the code: trace( typeof anArray[0] ); will output
"object." This can be a problem. If you try this: var
newClip:MovieClip = anArray[0]; you get a type mismatch from the
compiler. "Found Object where MovieClip is required." It
necessitates this: var newClip:MovieClip = MovieClip( anArray[0] );
Bummer no?
Ok. So fast forward. Lets assume a class List that uses an
array to hold the items in the list. So the class uses the Array
class in "composition." So you have methods like insert( ); and
retrieve(). Retriece() returns an item from an index in the array.
Because of the aforementioned problem, no matter what type the
thing was going into the list it comes out with type Object because
the retrieve function must return an item of some type, the only
option is to declare the return type of the retrieve() function as
Object. Lets say you know that this is a list of Strings. You could
write the retrieve()'s code like: return String( returnItem ); And
type the object "on the way out" .. but what if you want the list
to work with any type object, you would have to have a variable to
hold the desired type of objects in the list. And then as the
objects are being returned, you'd cast them to the type stored in
that variable. I guess that you'd pass the type to the constructor
of the List: var aList:List = new List( "AddressCard" ); -- That
should declare a List (Array) of AddressCards.
Is there a way to do this? have the type specified in casting
be dynamic?
And the flip-side of that is detecting the name of the class
of an object instance. The thing here would be to try to derive a
String from the name of the constructor function. (which is always
the class name) In actionscript 3 there is a service package--
mx.util -- I think, that has a function to return the qualified
class name of an object. But is there a jimmy rig for this in AS2?
My actual project does not use an Array to implement List. (
or Stack ) It uses a structure called a "linked list" - which is a
whole other topic, but same problem as with Arrays is also present
in the linked list versions and so requires the same solution. If
one is willing to type things explicitly when assigning an item in
the list to a variable of some type, this thing is quite excellent.
But I don't like it. I have the package with docs, code, sample
fla's, diagrams and everything that I would encourage people to
download, look at, try and whatever and then come back here with
any thoughts on it. There is a component with Flash professional
that is a list like structure, but it's so general that it crosses
the line into bloat. Ie: if you are using a list as a stack, you
only need getTop() and pop() and push() not all the other (12 or
so) methods in the class. Mine are patterned after structures from
the C++ standard template library. And the code style is C++, but I
think it's actually easier to read that way.
the files:
http://www.null.bz/ADL_Lib/ADT_Lib.zip
Thanks in advance, for your efforts! I really appreciate all
of it, helpful or not.

Answer 1

First reactions:
>>var newClip:MovieClip = MovieClip( anArray[0] );
Even though you must use a cast to prevent the compile time
error, you don't get an error on this line because the compiler
skips typechecking for values accessed with the [] operator.
>>Is there a way to do this? have the type specified in
casting be dynamic?
Nope. You must effectively type check all objects used
through array elements yourself.
Reading on...