(Resolved) Compatibility and generics

[cormac]

If Set is a generic interface, should the types

Set.<*> and Set.<int> be compatible?

[lth]

My view has been that the type represented by a type application is the parameterized type with the type arguments substituted. This model is simple and intuitive, which is probably its main feature.

A consequence of this is that the rules for type compatibitity follow immediately. If Set is defined as

  type Set.<T> = [T]

then I guess if [*] and [int] are compatible then Set.<*> and Set.<int> are compatible too. Ditto if Set is defined as

  class Set.<T> { ... }

then they would not be compatible (since Set.<int> and Set.<*> are both nominal subclasses of Object, not of Set.<T>).

[cormac]

That all makes sense, but in the case where

   class Set.<T> { ... }

we also have the option of saying that Set.<int> and Set.<*> are compatible. This would fit neatly into our framework.

But perhaps we should start with a smaller compatibility relation, and develop a list of potential extensions.

[cormac]

Resolved that this notion of compatibility will be supported.

[graydon]

Sorry, resolved that lth's notion of compatibility will be supported, or that your proposed one will be supported? I do not remember the outcome here. I vote with lth on this.

[lth]

Cormac/Graydon, this needs work before the f2f.

[lth]

After some conversation in email (and with Jeff here), we're coming to the conclusion that we do the simple thing for ES4: Set.<int> and Set.<*> are not related. Let's keep it simple for now.

Revisiting this for ES5 seems the right thing.

[lth]

It is possible to resolve bugs as "Deferred" in Trac. On the other hand it might be just as useful to keep a more structured document of deferred ideas, to collect what's on the wiki and what's come up over the years.

For the moment I suggest that you open a new bug (because I'd like to keep this until we've started writing) on the issue, then resolve it as deferred, then when we have time we'll go over them and record them properly. I've been doing a lot of writing lately but I doubt I have time for one more paper right now.