Re: Receiver class does not define or inherit an implementation of the resolved method

[Per Bothner <per@bothner.com>]

On 8/29/21 12:03 PM, Phil Eaton wrote:> Still new to Kawa. I'm trying to implement an interface (
> io.jooby.Route$Handler
> <https://github.com/jooby-project/jooby/blob/2.x/jooby/src/main/java/io/jooby/Route.java#L247>).
> It only has a single non-default method, apply.
> 
> Here's what I've got
> 
> (define (route app method path handler)
>    (let ((handler (object (io.jooby.Route$Handler)
>                           #| This method exists just to stop Jooby from
> trying to introspect Java code that doesn't exist because this isn't
> written in Java. |#
>                           ((apply (ctx ::io.jooby.Context)) ::string
>                            #!null)
>                           ((apply (ctx ::io.jooby.Context))
> ::java.lang.Object
>                            (handler ctx)))))
>      (app:route method path handler)))
> 
> 
> But when this gets exercised, I get:
> 
> [worker-1-3] ERROR io.jooby.Jooby - GET /hello-world 500 Server Error
> java.lang.AbstractMethodError: Receiver class main$0 does not define or
> inherit an implementation of the resolved method 'abstract java.lang.Object
> apply(io.jooby.Context)' of interface io.jooby.Route$Handler.

I don't see anything obviously wrong.  One thing to try is instead of an
anonymous class (with object) use a named class (with define-simple-class).
The anonymous class is more convenient of course there is some extra "magic"
(such as invisible fields) that might complicate things.

> Also on a tangent, I was excited about the lambda shorthand for single
> method objects. Like I said this interface only has a single non-default
> method: apply. But I tried just calling `(app:route method handler)`
> without wrapping it in the io.jooby.Route$Handler object but it still
> failed. I guess it couldn't figure out this one method.

Kawa has to be able to figure out at compile time that a specific class/interface
is required before it can convert the lambda to an object.  (As far as I can
remember, doing this conversion at run-time isn't implemented, and would be
fairly complicated.)  So you may need to add some more type-specifiers.

I suggest using javap to look at the generated classes, to see what is going on.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/