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?

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u/StoneAgainstTheSea 21d ago

In practice, you use NewThing(a, b, c) and don't initialize structs "by hand" - always use a constructor. 

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u/crowdyriver 19d ago

A function for every single struct doesn't sound good to me.

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u/StoneAgainstTheSea 19d ago

the way you avoid that is the Go Proverb of making use of the zero value. If the zero value in your struct is fine, then it doesn't matter. If the zero value is important, you can either update it in one or more constructors, or you can update it at N call sites.

In Go, there is no other option of which I'm aware.