DeepEqual []interface{}

Question

Looking at the following golang code:

b := []byte(`["a", "b"]`)
var value interface{}
json.Unmarshal(b, &value)
fmt.Println(value)                 // Print [a b]
fmt.Println(reflect.TypeOf(value)) //Print []interface {}
var targetValue interface{} = []string{"a", "b"}
if reflect.DeepEqual(value.([]interface{}), targetValue) {
    t.Error("please be equal")
}

Am I expecting too much of DeepEqual? Reading the documentation, the following statements reinforce my assumption that it should work:

Array values are deeply equal when their corresponding elements are deeply equal.
Interface values are deeply equal if they hold deeply equal concrete values.
Slice values are deeply equal when (...) or their corresponding elements (up to length) are deeply equal.

What am I missing here?

You may find these interesting. [Package for equality of Go values: google/go-cmp](https://github.com/google/go-cmp). [Life of a Go Infrastructure Maintainer](https://medium.com/@zombiezen/life-of-a-go-infrastructure-maintainer-cb1419308eb5). — peterSO, Mar 06 '18 at 15:57

score 5 · Answer 1 · answered Mar 06 '18 at 14:36

5

You're comparing a []interface{} against []string, which should never be equal.

if reflect.DeepEqual(value.([]interface{}), targetValue) {

compared against targetValue which is of type []string:

var targetValue interface{} = []string{"a", "c"}

answered Mar 06 '18 at 14:36

Jonathan Hall

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Understood. I assumed they would both be interfaces, or both []string. I guess this would fall under "Values of distinct types are never deeply equal.". What can I do to make them of the same type to I can compare? – Nathan H Mar 06 '18 at 14:41
Got it! Instead of declaring my targetValue with literal values, I use `append()`. Doing this preserves the `[]interface{}` type. – Nathan H Mar 06 '18 at 14:51
2

The easy way in your specific case would be: `var targetValue interface{} = []interface{}{"a", "b"}` – Jonathan Hall Mar 06 '18 at 14:52
Indeed that's even better. Can you update your answer? – Nathan H Mar 06 '18 at 14:54
yeap, as @Flimzy mentioned, if you declare it as []interface{}, then the types would be same and hence, reflect would deep equal should give out true - https://play.golang.org/p/iN3STrExW64 – vedhavyas Mar 06 '18 at 14:55
@Flimzy can you update your answer with your suggestion, so the answer will be complete? – Nathan H Mar 07 '18 at 07:30

DeepEqual []interface{}

1 Answers1