`IsZero()` and `ToNullUUID` Helper Functions

[falsaffa]

Summary

Suggest adding a couple helper functions.

IsZero

IsZero() allows uuid to support the Nullable interface and interface better with existing code. It can be as simple as:

func (u UUID) IsZero() bool {
    return u == Nil
}

This is particularly important when interfacing UUID with the existing ORM libraries. Heck, IsZero() is even used by the reflect package too!

ToNullUUID

Another helper function that is used by this null package (and is quite convenient) are to-null values from the original primitives. So in the case of uuid.UUID and uuuid.NullUUID, adding the following helper function.

func ToNullUUID[T uuid.UUID | uuid.NullUUID](id T) uuid.NullUUID {
	if v, ok := any(id).(uuid.UUID); ok {
		if v == uuid.Nil {
			return uuid.NullUUID{}
		}

		return uuid.NullUUID{v, true}
	} else if v, ok := any(id).(uuid.NullUUID); ok {
		return v
	} else {
		panic("this should not happen")
	}
}

That way we don't have to write the following code:

id := uuid.New()

// If you know that id is not nil
nullVal := uuid.NullUUID{id, true}

// if you don't know whether or not id is nil.
nullVal := uuid.NullUUID{id, id == uuid.Nil}

// And if you want to use named struct fields
nullVal := uuid.NullUUID{UUID: id, Valid: id == uuid.Nil}

// What it looks like with the helper function
nullVal := uuid.ToNullUUID(id)

This is particularly useful when combined with existing libraries such as ORMs. Casting to uuid.NullUUID is common.

[matwachich]

I had a similar problem in a DB (SQLite), where I have FK to UUIDs

I have a table where the FK can be NULL (not linked to any parent record), and passing a uuid.Nil caused a FK constraint violation.

It seems to me more logic that a uuid.Nil is stored as NULL in a database. But It's only my personal use case... so not sure at all.