The most common cause of issues like this is if you reload ns1 after
loading ns2, then T2 will be implementing an "old" version of pro-1,
while fun will be testing for satisfaction of the "current" version.
On Oct 15, 8:04 am, Eric in San Diego <eric.sc...@acm.org> wrote:
> Hi all -
>
> I'm experiencing some unexpected behavior with protocols. Stripping
> out extraneous details...
>
> ;;;;;;;;;;;;;
> (ns my.ns1
> ...)
>
> (defprotocol pro-1
> ...)
>
> (deftype T1 [...]
> pro-1
> ...)
>
> (defn fun [p]
> ^{:pre [(satisfies? pro-1 p)
> ]
> }
> ...)
> ;;;;;;;;;;;;;;;;
> Then in another file:
> (ns my.ns2
> (:use [my.ns1]))
>
> (deftype T2 [...]
> pro-1
> ...)
>
> ...
> ;;;;;;;;;;;;;;;;;;;;;;;;;
> Then in a third file
> (ns my.ns3
> (:use
> [my.ns1]
> [my.ns2]))
>
> (defn ...
> (let [x (T2. ...)
> ]
> ...
> (fun x)
> ...))
>
> This throws an error saying that 'x' does not satisfy the protocol.
>
> Looking at the documented source of 'satisfies?', I see that this
> amounts to asking
> (instance? (:on-interface pro-1) x), which => false.
>
> (:on-interface pro-1) => my.ns1.pro_1
>
> but (class x) => T2 and (supers T2) => #{my.ns1.pro_1
> java.lang.object}
>
> Also, just to check (instance? T2 x) => true.
>
> What am I not getting here? How can x be an instance of T2 and not be
> an instance of one of its supers?
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