Is it possible to define equality for named types/structs?

Question

After reading a related question about using slices in maps, I became curious about equality in Go.

I know it's possible to override the equals method of a Java Object. Is there a similar way to define how Go checks user defined types/structs for equality? If so, there would be a workaround for the issue referenced above. I thought using interface{} values might offer a solution but I received the error message panic: runtime error: hash of unhashable type []int.

Answer 1

No. You can't modify the equality operator and there is no built-in way to add support for custom types to use == syntax. Instead you should compare the pointer values using reflect.DeepEqual.

Go supports equality checking structs.

type Person struct {     Name string }  a := Person{"Bill DeRose"} b := Person{"Bill DeRose"}  a == b // true 

It won't work with pointer fields (in the way you want) because the pointer addresses are different.

type Person struct {     Friend *Person }  a := Person{Friend: &Person{}} b := Person{Friend: &Person{}}  a == b // false   import "reflect"  a := Person{Friend: &Person{}} b := Person{Friend: &Person{}}  reflect.DeepEqual(a, b) // true 

Keep in mind there are caveats.

In general DeepEqual is a recursive relaxation of Go's == operator. However, this idea is impossible to implement without some inconsistency. Specifically, it is possible for a value to be unequal to itself, either because it is of func type (uncomparable in general) or because it is a floating-point NaN value (not equal to itself in floating-point comparison), or because it is an array, struct, or interface containing such a value.