Add Copy() and IsZero() methods

[sjansen]

These functions help to make custom marshalling and unmarshalling code easier to read.

[peterbourgon]

I'm not necessarily against these changes, but I wonder if they're valuable enough to expand the API surface area. @tsenart ?

[peterbourgon]

It's confusing that a method named Copy would mutate the receiver — Copy should return a ULID value.

[sjansen]

I'm implementing a third-party unmarshalling interface. Returning a value doesn't work, mutating an existing struct field is basically a requirement. However, as I was working on a simplified example I realized how to make my implementation sufficiently readable as is.

You have a good point about mutating the caller being surprising. I could either remove the method, or replace it with a function: Copy(dst &ULID, src ULID), if you think it could be helpful to future users.

I assume IsZero() is acceptable?

While neither change is strictly necessary, I do feel they improve readability and reduce coupling to the underlying byte array implementation.

[peterbourgon]

Actually, on reflection, I don't think IsZero is a good idea, because a zero value ULID is still a valid ULID.

[sjansen]

That's an odd opinion given IsZero isn't about invalid / valid but instead default / non-default, which users can choose to interpret as uninitialized / initialized.

As the system implementer, isn't it my prerogative to decide if the zero value is valid or not in my system?

[peterbourgon]

That's an odd opinion given IsZero isn't about invalid / valid but instead default / non-default . . .

My understanding is that a type with an IsZero method is not usable in it's zero-value state, which is not the case for ULIDs. Is that understanding incorrect?

[sjansen]

January 1st, year 1 is a perfectly valid date.
https://golang.org/pkg/time/#Time.IsZero

Perhaps you are confusing IsValid and IsZero.
https://golang.org/pkg/reflect/#Value.IsValid
https://golang.org/pkg/reflect/#Value.IsZero

Checking if id.IsZero is essentially that same as checking count == 0 or password == "", the values are valid but depending on business rules they may not be acceptable.

[peterbourgon]

If that's true then why doesn't every type offer an IsZero method?

n.b. you don't need to use Compare to test equality

var u1, u2 ulid.ULID
println(u1 == u2) // prints true

[peterbourgon]

@sjansen

I'm implementing a third-party unmarshalling interface.

Can you say a bit more about your use case? I bet we can figure something out.

[sjansen]

Can you say a bit more about your use case? I bet we can figure something out.

Thanks, but I've already got a solution I'm happy with and I've moved on.