Re: light weight types

Joshua Cranmer <Pidgeot18@verizon.invalid>
Mon, 05 Oct 2009 15:32:24 -0400
On 10/05/2009 12:33 PM, Roedy Green wrote:

On Sat, 03 Oct 2009 21:34:46 -0400, Joshua Cranmer
<Pidgeot18@verizon.invalid> wrote, quoted or indirectly quoted someone
who said :

Types can also be recursive. A recursive type is something of the form
class Foo<T extends Foo<T>>. You generally subclass or implement
interfaces of these form in the fashion class Bar extends Foo<Bar>. The
purpose of a recursive type is to operate on itself in some fashion:
think of Comparable's compareTo method. Classes implementing Comparable
only compare objects of the same class as them, not of other classes
implementing Comparable.

I don't understand. I looked at the definitions of Comparable and
Comparator, compare, compare to, and their implementations. I saw no
use of recursive types.

I keep forgetting that it's defined as Comparable<T>, not Comparable<T
extends Comparable<T>>. Enum is actually defined recursively; Comparable
is just typically used in such a manner. I had also planned to motivate
<? super T> (with the canonical example for such bounds, <T extends
Comparable<? super T>>) here, but changed my mind later.

Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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