How to make an addressable getter that casts from an interface

I have the concept of Context which is a map that can hold any structure. Basically, I want to create a generic getter that adddressably 'populates' the destination interface (similarly to how json decoding works).

Here's an example of how I want this to work:

type Context map[string]interface{}

// Random struct that will be saved in the context
type Step struct { 
	Name string
}

func main() {
	stepA := &Step{Name: "Cool Name"}

	c := Context{}
	c["stepA"] = stepA

	var stepB *Step
	err := c.Get("stepA", stepB)
	if err != nil {
		panic(err)
	}

	fmt.Println(stepB.Name) // Cool Name
	stepB.Name = "CoolName2"

	fmt.Println(stepA.Name) // I want to say: CoolName2
}

func (c Context) Get(stepId string, dest interface{}) error {
	context, ok := c[stepId]
	if !ok {
		return nil
	}

	destinationValue := reflect.ValueOf(dest)
	contextValue := reflect.ValueOf(context)

	destinationValue.Set(contextValue) // Errors here
	return nil
}

I leaned towards using reflect, but maybe I don't need it? - so opened to other suggestions (except for generics as that complicates other matters) I'm getting the following error with the above:

panic: reflect: reflect.Value.Set using unaddressable value

You can test it here.

The argument passed to Get must be a pointer type whose element type is identical to the type in the context map. So if the value in the context map is of type *Step, then the argument's type must be **Step. Also the passed in argument cannot be nil, it can be a pointer to nil, but it itself cannot be nil.

So in your case you should do:

var stepB *Step
err := c.Get("stepA", &stepB) // pass pointer-to-pointer
if err != nil {
	panic(err)
}

And the Get method, fixed up a bit:

func (c Context) Get(stepId string, dest interface{}) error {
	context, ok := c[stepId]
	if !ok {
		return nil
	}

	dv := reflect.ValueOf(dest)
	if dv.Kind() != reflect.Ptr || dv.IsNil() {
		return errors.New("dest must be non-nil pointer")
	}

	dv = dv.Elem()
	cv := reflect.ValueOf(context)
	if dv.Type() != cv.Type() {
		return errors.New("dest type does not match context value type")
	}

	dv.Set(cv)
	return nil
}

https://go.dev/play/p/OECttqp1aVg