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

i have particular go lang struct object i'm interacting , expect equal itself. i'm passing function function returns 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, see tiger , output_tiger appear same , evaluate equal. great. that's expect. now, try using definition yummyfood

type yummyfood {     calories int     ingredients []string } 

all of sudden, output echo_back not evaluate same input, type assertion. 'panic: runtime error: comparing uncomparable type yummyfood'

the question why addition of []string type cause input , output uncomparable? how can modify output_tiger same thing put in (i.e expect same 'tiger'). how reflect output_tiger make equal tiger?

slices ([]string) has no equality defined. arrays , structs contains members has equality defined have equality defined.

note equality still undefined slices, calculation in general infeasible. note ordered comparison operators (< <= > >=) still undefined structs , arrays.

from http://golang.org/doc/go1.html#equality