[go-nuts] Compiler error when using an interface type in a list

[John Sturdy]

I've defined an interface type, and a concrete type that I think implements 
that interface, but when I use it in a list, I get an error from the 
compiler that makes it look like it doesn't.

Here's my interface type, in anything/anything.go:

    package anything

    import (
            "fmt"
    )

    type AnyThing interface {
            Textual() string
            Numeric(name string) int
    }

    func OneCallee(thing AnyThing) {
            fmt.Printf("textual result is %s and numeric result is %d\n", 
thing.Textual(), thing.Numeric("default"))
    }

    func ListCallee(things []AnyThing) {
            fmt.Printf("textual result is %s and numeric result is %d\n", 
things[0].Textual(), things[0].Numeric("default"))
    }


and here's a concrete type that defines the methods required by the 
interface, in particularthing/particularthing.go:

    package particularthing

    type ParticularThing struct {
            Name string
            Number int
    }

    func (n ParticularThing) Textual() string {
            return n.Name
    }

    func (n ParticularThing) Numeric(name string) int {
            return n.Number
    }

and here's the caller:

    package main

    import (
            "example.com/user/scratch/anything"
            "example.com/user/scratch/particularthing"
    )

    func main() {
            onething := particularthing.ParticularThing{"this", 1}
            anything.OneCallee(onething)
            thinglist := make([]particularthing.ParticularThing, 1)
            anything.ListCallee(thinglist)
    }

When I compile it, I get:

    ./caller.go:12:21: cannot use thinglist (type 
[]particularthing.ParticularThing) as type []anything.AnyThing in argument 
to anything.ListCallee

Could some explain what the problem with this is?

I've attached a tarball of the files to make experimental changes easier.

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minimal.tar
Description: Unix tar archive