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.

There's no standard in Go language itself, yet (go 1.13).

However, comparison utilities could provide their own way to support it.

Function cmp.Equal (from google/go-cmp/cmp) supports definition of custom type comparator via definition of a Equal method:

• If the values have an Equal method of the form "(T) Equal(T) bool" or "(T) Equal(I) bool" where T is assignable to I, then use the result of x.Equal(y)even if x or y is nil. Otherwise, no such method exists and evaluation proceeds to the next rule.