WHwhateveracct·Feb 28, 2020
Here's an example of why Go's simplicity is complicated:
Say I want to take a uuid.UUID [1] and use it as my id type for some database structs.
At first, I just use naked UUIDs as the struct field types, but as my project grows, I find that it would be nice to give them all unique types to both avoid mixups and to make all my query functions clearer as to which id they are using.
type DogId uuid.UUID
type CatId uuid.UUID
I go to run my tests (thank goodness I have tests for my queries) and everything breaks! Postgres is complaining that I'm trying to use bytes as a UUID. What gives? When I remove the type definition and use naked UUIDs, it works fine!
The issue is Go encourages reflection for this use-case. The Scan() and Value() methods of a type tell the sql driver how to (de)serialize the type. uuid.UUID has those methods, but
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when I use a type definition around UUID, it loses those methods.
So the correct way to wrap a UUID to use in your DB is this:
type DogId struct { uuid.UUID }
type CatId struct { uuid.UUID }
Go promised me that I wouldn't have to deal with such weird specific knowledge of its semantics. But alas I always do.
[1] https://github.com/google/uuid
EDIT: This issue also affects encoding/json. You can see it in this playground for yourself! https://play.golang.org/p/erfcSIe-Z7b
EDIT: I wrongly used type aliases in the original example, but my issue is with type definitions (`type X Y` instead of `type X = Y`). So all you commenters saying that I did the wrong thing, have another look!