clarification of 18.2.3

[Dan Smith]

On Oct 29, 2013, at 1:11 PM, "Rafkind, Jon" <jon.rafkind at hp.com> wrote:

> Section 18.2.3 Subtyping Constraints of jsr 335 says
> 
> A constraint formula of the form ⟨S <: T⟩ is reduced as follows:
>  ...
>  If T is a non-parameterized class or interface type, C, then the constraint reduces to true if S is a parameterization of C, or if C is a superclass or superinterface of T, and false otherwise.
> 
> 1. What is the point of introducing a new metavariable C? It seems that C == T

Just a stylistic thing to distinguish general types from classes.  But you're probably right that it would be better to avoid the extra variable.

> 2. I assume the point of this rule is to handle the case where a type has T does not have type parameters even though its class declaration has them:
> 
> List<a1> <: List
> 
> Where a1 is some inference variable. In this case, any parameterization of List is a subtype of List. Is that right?

Yes.

> 3. The last clause seems vacuous. 'if C is a superclass/superinterface of T' but C == T, so assuming superclass/superinterface means a proper super then C can never be its own super type. Also this leaves S out. Is it a typo, and it should instead read as
> 
> 'or if C is a superclass or superinterface of S ...'
> 
> Which would handle the case of
> 
> List<a1> <: Collection

Yes, it's a typo.  Thanks for noting it.

—Dan