On Tue, 20 Jun 2000, Karl Ramberg wrote:

> Hi,
> 	I've been wondering why variables don't default to something meaningful
> 	in their context,

They do...nil. The context being "uninitialized" :)

> when they are not initialized. Smalltalk is a untyped
> 	language but it still requires types when the variables are uninitiated. 
> 	If for example the variable recognizes it's context it could default
> 	to something like: 
> 
> 	a == nil == false == 0 == '' == empty collection or bag or what ever.

Er..because they are all different things?
 
> 	Then one could use these examples without telling the number value or
> 	Boolean .
> 	
> 	a + 2  => 2 	"a defaults to 0"

But *why* default to *0*? #+ is a message send, so you don't *know* that
it *should* go to 0. Furthermore, it would make initializtion bugs
invisible:

	a := self valueFromSomeSourceAndIsUsuallyZero.
	^a + 2

How could you (easily) tell between valueFromSomeSourceAndIsUsuallyZero
*correclty* returning 0 and *erroneously* returning nil?

(If you respond, "But there's an *assignment* up there", I'll respond, but
what if the "assignment" took place inside
valueFromSomeSourceAndIsUsuallyZero...it wouldn't be visible to this
method.)

If you want default *instance variables* that's easy enough with lazy
initialization (you, uh, *do* use access? :))

And if it's a *temporary*, then I don't see why this is an advantage at
all.

> 	a
> 	 ifTrue:[]		"a defaults to false"

Why is this good? Why not default to true?

	a
	  ifFalse:[]
???

> 	It is probably several reasons to not make the system like this, but
> 	from a beginners perspective it makes sense. 

I think you'd want to distinguish between this for temps and this for
access object variables. You could, perhaps, have method context dependant
initializtion of ivars. But I think trying to infer from immediate
*lexical* context is a bad idea...

...aside from complicating things enormously to do at all, much less
"right" (if there *is* a right), I'm not sure what the advantages are?

Could you spell out what advantages you see with the scheme?

Cheers,
Bijan Parsia.