Constraints on type parameters in method formals aren't added to the environment used to typecheck the method body

This is a bug in propagating type constraints from method arguments into the environment. A workaround for now is to move the type constraint into the method guard, namely:

import x10.util.Ordered;
public class LessIsMore {
  static def doIt[T](a: T){T <: Ordered[T]} {
    return a < a;
  }
}

Thanks. It does work in my "real" code. It occurred to me that there is a situation where you really might want to attach the constraint to the argument.

def doIt[T]{a:T{T <: Ordered[T]}, b: T) { /* need "a" ordered, but not b */ }

Not all subtypes of T need implement Ordered[T], but it may be important that the first argument should. So it does make sense to put some effort into fixing the constraint propagation.

Sorry, it doesn't work that way. You are not constraining a and b, you are constraining T. And the constraint is in effect for the whole method. So either both a and b are ordered, or neither is (because they are the same type, T). Since T is defined by doIt(), you may as well put the constraint into the method guard.

If you want two potentially different types, you have to use two different type variables.

The meaning you tried to assign to this idiom above is actually captured by XTENLANG-683.

Again thanks: I'll make sure I explain this clearly in the Guide.

Defer to 2.2.1.

bulk defer of open issues to 2.2.2.

bulk defer of issues to 2.2.3.

bulk defer of 2.3.0 open issues to 2.3.1.

bulk defer to 2.3.2