Agfdhyk

I want to check that two structs are equal, but have some problem:

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

You can use reflect.DeepEqual, or you can implement your own function (which performance wise would 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))

reflect.DeepEqual is often incorrectly used to compare two like structs, as in your question.

cmp.Equal is a better tool for comparing structs.

To see why reflection is ill-advised, let's look at the documentation:

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

....

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

If we compare two time.Time values of the same UTC time, t1 == t2 will be false if they're metadata timezone is different.

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

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

Here's how you'd roll your own function http://play.golang.org/p/Qgw7XuLNhb

func compare(a, b T) bool {

  if &a == &b {

    return true

  }

  if a.X != b.X || a.Y != b.Y {

    return false

  }

  if len(a.Z) != len(b.Z) || len(a.M) != len(b.M) {

    return false

  }

  for i, v := range a.Z {

    if b.Z[i] != v {

      return false

    }

  }

  for k, v := range a.M {

    if b.M[k] != v {

      return false

    }

  }

  return true

}