[thomas11]

Right. You could always define a new type with an existing underlying type, like Celsius with the underlying type int in your example. See the spec here: https://golang.org/ref/spec#Types

This would define a new, non-interchangeable type, even though it's just an int behind the scenes. The new type alias on the other hand define a new name for an existing type; you still have just one type. In the user ID example above that's not what you want, it would allow using an int where a UserID is required.

[frou_dh]

As I understand it, there have been a couple of compiler-blessed aliases for a long time (byte -> uint8 and rune -> int32), making this a similar thing but now at user level.