How to compare struct, slice, map are equal?

Question

I want to check that the two structures are equal, but have some problems:

package main import ( "fmt" "reflect" ) type T struct { X int Y string Z []int M map[string]int } func main() { t1 := T{ X:1, Y:"lei", Z:[]int{1,2,3}, M:map[string]int{ "a":1, "b":2, }, } t2 := T{ X:1, Y:"lei", Z:[]int{1,2,3}, M:map[string]int{ "a":1, "b":2, }, } fmt.Println(t2 == t1) //error - invalid operation: t2 == t1 (struct containing []int cannot be compared) fmt.Println(reflect.ValueOf(t2) == reflect.ValueOf(t1)) //false fmt.Println(reflect.TypeOf(t2) == reflect.TypeOf(t1)) //true //Update: slice or map a1 := []int{1,2,3,4} a2 := []int{1,2,3,4} fmt.Println(a1==a2) //invalid operation: a1 == a2 (slice can only be compared to nil) m1 := map[string]int{ "a":1, "b":2, } m2 := map[string]int{ "a":1, "b":2, } fmt.Println(m1==m2) // m1 == m2 (map can only be compared to nil) } 

http://play.golang.org/p/AZIzW2WunI

Answer 1

You can use reflect.DeepEqual , or you can implement your own function (which will be better than using reflection):

http://play.golang.org/p/CPdfsYGNy_

 m1 := map[string]int{ "a":1, "b":2, } m2 := map[string]int{ "a":1, "b":2, } fmt.Println(reflect.DeepEqual(m1, m2)) 

Answer 2

reflect.DeepEqual often misused to compare two similar structures, as in your question.

cmp.Equal is the best tool for comparing structures.

To understand why reflection is not recommended, review the documentation :

Struct values ​​are deeply equal if their respective fields, both exported and unexported, are deeply equal.

....

numbers, bools, strings and channels are deeply equal if they are equal using the Go == operator.

If we compare two time.Time values ​​of the same UTC time, t1 == t2 will be false if they are the time zone of the metadata.

go-cmp looks for the Equal() method and uses it to correctly compare time.

Example:

 m1 := map[string]int{ "a": 1, "b": 2, } m2 := map[string]int{ "a": 1, "b": 2, } fmt.Println(cmp.Equal(m1, m2)) // will result in true 

Answer 3

Here is how you would apply your own function http://play.golang.org/p/Qgw7XuLNhb

 func compare(a, b T) bool { if &a == &b { return true } if aX != bX || aY != bY { return false } if len(aZ) != len(bZ) || len(aM) != len(bM) { return false } for i, v := range aZ { if bZ[i] != v { return false } } for k, v := range aM { if bM[k] != v { return false } } return true }