Is it possible to define equality for named types/structs?
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.
No, this is not user-definable. Go has strict rules what counts as equal, and even what is comparable which itself is based on assignability. Take a look at the Comparison operators section of the spec.