generics - Limit function parameter argument to base class in Swift -

assume following setup:

class baseclass<t> { }  class subclass<t>: baseclass<t> { }  infix operator >-- { associativity left }  func >-- <t>(lhs: baseclass<t>, rhs: subclass<t>) {     // here } 

what looking way exclude subclass being used lhs argument operator >--. kind of negative type constraint on generic argument - i.e., t: baseclass t != subclass:

func >-- <t, b: baseclass<t> b != subclass<t>>(lhs: b, rhs: subclass<t>) 

but not appear there != argument can supply negative type constraint generic. there way this?

thanks!

edit:

i think can make question less complicated - think following setup gets @ same issue without distracting details:

class baseclass { } class subclass: baseclass { }  // want able do, don't know how // or if possible: func dosomething<b: baseclass b != subclass>(arg: b) { } 

hope didn't confuse more, "infix operator" part , fact baseclass generic baseclass<t> aren't important question...

you cannot prevent substitution of subclass instance superclass instance @ compiler level, trying do, because substitution basis of polymorphism itself.

you are, of course, free throw wobbly at runtime if dynamictype of parameter turns out not superclass:

func dosomething(arg: baseclass) {     if !(arg.dynamictype === baseclass.self) {         fatalerror("die die die")     }     println("ok") }