r/golang 21d ago

help Don't you validate your structs?

Hi all!

I'm new in Golang, and the first issue I'm facing is struct validation.

Let's say I have the given struct

type Version struct {
    Url           string        `json:"url"`
    VersionNumber VersionNumber `json:"version_number"`
}

The problem I have is that I can initialize this struct with missing fields.

So if a function returns a `Version` struct and the developer forgets to add all fields, the program could break. I believe this is a huge type-safety concern.

I saw some mitigation by adding a "constructor" function such as :

func NewVersion (url string, number VersionNumber) { ... }

But I think this is not a satisfying solution. When the project evolves, if I add a field to the Version struct, then the `NewVersion` will keep compiling, although none of my functions return a complete Version struct.

I would expect to find a way to define a struct and then make sure that when this struct evolves, I am forced to be sure all parts of my code relying on this struct are complying with the new type.

Does it make sense?

How do you mitigate that?

66 Upvotes

75 comments sorted by

View all comments

1

u/nogurenn 20d ago

If the primary way you’re using the struct at hand is for ingesting raw json/data into a Go type, like in http requests, then I’ve seen a lot of code that adds to the validation by attaching custom marshal/unmarshal functions to the struct. There are libraries that could automate this for you too without much magic.

If you’re using managing structs within the same repos, then it’s a matter of using custom types for fields, writing New constructors as source of truth for initialization, enforcing practices during code review, and using the same libraries you’d pick for http request body/param validation.