Re: "" : List[String]

On Apr 27, 2010, at 11:03, Thomas Leonard wrote:

> This surprised me:
>
> ? "" : List[String]
> # value: ""
>
> ? "" : List[int]
> # value: []
>
> I was calling TreeItem.setText(str). When str is the empty string it
> coerces to a list of strings and you get "Ambiguous overload on class
> org.eclipse.swt.widgets.TableItem: setText(String) vs
> setText(String[])".
>
> Is this intentional?

It isn deliberate that String is a subtype of ConstList.

I do not care for this choice, because things which want lists usually  
don't want strings-of-characters, and because it breaks the property  
we would otherwise have that if a :List and b :List have the same  
elements, they are ==.

The list guard returning "" is evidently because the "cheap success"  
case in ListGuard passed, because the element guard is a ClassDesc.  
That this code has this behavior in one optimization-based case and  
not in another seems to me more evidence that "" being a ConstList is  
a bad idea.

(Having String be a subtype of EList, the mutable-or-immutable-list  
type, would seem to me to serve the same acknowledge-the-protocol- 
inheritance purpose and be safer.)

But, I wouldn't want to make this kind of significant change without  
consulting MarkM.

-- 
Kevin Reid                                  <http://switchb.org/kpreid/>