How to know if a variable of arbitrary type is Zero in Golang?

Question

Because not all types are comparable, e.g. a slice. So we can\'t do this

var v ArbitraryType
v == reflect.Zero(reflect.TypeOf(v)).Interface()

Answer 1

Both of the following give me reasonable results (probably because they're the same?)

reflect.ValueOf(v) == reflect.Zero(reflect.TypeOf(v)))

reflect.DeepEqual(reflect.ValueOf(v), reflect.Zero(reflect.TypeOf(v)))

e.g. various integer 0 flavours and uninitialized structs are "zero"

Sadly, empty strings and arrays are not. and nil gives an exception.
You could special case these if you wanted.

Answer 2

As Peter Noyes points out, you just need to make sure you're not comparing a type which isn't comparable. Luckily, this is very straightforward with the reflect package:

func IsZero(v interface{}) (bool, error) {
    t := reflect.TypeOf(v)
    if !t.Comparable() {
        return false, fmt.Errorf("type is not comparable: %v", t)
    }
    return v == reflect.Zero(t).Interface(), nil
}

See an example use here.

Answer 3

Go 1.13 introduced Value.IsZero method in reflect package. This is how you can check for zero value using it:

if reflect.ValueOf(v).IsZero() {
    // v is zero, do something
}

Apart from basic types, it also works for Chan, Func, Array, Interface, Map, Ptr, Slice, UnsafePointer, and Struct.

Answer 4

See this post:

Golang: Reflection - How to get zero value of a field type

Basically you need to have special cases for the non comparable types.