Uncomparable type error when []string field used (Go lang)

Question

I have a particular Go lang struct object that I'm interacting with and I expect it to be equal to itself. I'm passing the function to a function that simply returns it but that does it by accepting interface{} inputs/outputs

type Animal struct {
    name string
    food interface{}
}

type YummyFood {
    calories int
}

func echo_back(input interface{}) interface{} {
    return input
}

func main() {
    var tiger_food = Food{calories: 1000}
    var tiger = Animal{name: "Larry", food: tiger_food}
    output_tiger := echo_back(tiger)

    fmt.Printf("%T, %+v\n", tiger, tiger)
    fmt.Printf("%T, %+v\n", output_tiger, output_tiger)
    fmt.Println(tiger == output_tiger)
    fmt.Println(tiger == output_tiger.(Animal))

}

Running this, you see that the tiger and output_tiger appear to be the same and evaluate to be equal. Great. That's what I would expect. NOW, try using this definition for YummyFood

type YummyFood {
    calories int
    ingredients []string
}

All of a sudden, the output from echo_back does NOT evaluate to be the same as the input, even with the type assertion. I get 'panic: runtime error: comparing uncomparable type YummyFood'

The question is why does the addition of the []string type cause the input and output to be uncomparable? How can I modify output_tiger to get back the same thing I put in (i.e I expect it to be the same as 'tiger'). How do I reflect output_tiger to make it equal to tiger?

Answer 1

It won't be fast, but you can use reflect.DeepEqual() to compare the slices (or just YummyFood). It does the work to loop through it to compare all the elements. You could probably make a more efficient function to do it, but if the one that's there is fast enough you'll save yourself some work and maybe some bugs. :-)