[go-nuts] Trying to dynamically find interfaces

[David Koblas]

I've got a program that is trying to implement functions on "subclasses", 
where the parent can check to see if the interface is implemented. For 
perspective, it's really dealing with REST URL generation based on if 
methods exist.

What I'm running into is that based on the following pattern, both the 
IList and IGet interfaces are found on the TestController object, when only 
1 is implemented. When the IGet interface is called I get a panic.

I would rather not make concrete definitions of the Get/List on the base 
struct and then have to override them, would much rather do the test for 
existence then go from there.

Code is available on the playground --  https://play.golang.org/p/5j58fejeJ3

package main

import "fmt"

type IGet interface {
    Get(int)
}

type IList interface {
    List(int)
}

type Application struct {
    name    string
}

type BaseAppController struct {
    *Application

    IGet
    IList
}

type TestController struct {
    *BaseAppController
}

func (ctrl *BaseAppController) Init() {
    fmt.Println("In Init")

    if f, ok := interface{}(ctrl).(IGet); ok {
        fmt.Println("Controller Found GET", f)
    } else {
        fmt.Println("Controller NOT Found GET", f)
    }

    if f, ok := interface{}(ctrl).(IList); ok {
        fmt.Println("Controller Found LIST", f)
    } else {
        fmt.Println("Controller NOT Found LIST", f)
    }
}

func (ctrl *BaseAppController) Call() {
    fmt.Println("In Call")

    if f, ok := interface{}(ctrl).(IGet); ok {
        fmt.Println("Controller Found GET - going to call", f)

        f.Get(7)
    } else {
        fmt.Println("Controller NOT Found GET - can't call", f)
    }
}

// Test controller implements the Get Method
func (ctrl *TestController) Get(v int) {
    fmt.Printf("Hi name=%s v=%d\n", ctrl.name, v)
}

func main() {
    app := Application{"hithere"}
    ctrl := TestController{&BaseAppController{Application: &app}}

    ctrl.Init()

    ctrl.Call()
}

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