[technics256]

Is there any movement in the language spec to address this in the future with Nil types or something?

[baby]

I really love Golang and how it focused on making the job of the reader easy. But with today’s modern programming language the existence of null pointer dereference bugs doesn’t really make sense anymore. I don’t think I would recommend anyone to start a project in Golang today.

Maybe we’ll get a Golang 3 with sum types…

[aatd86]

If you squint really hard, the work on generics is a step toward the future.

If you don't squint, then I don't think so.

[mcronce]

With generics, can you not make a NonNil<T> struct in Go, where the contents of the struct are only a *T that has been checked at construction time to not be nil, and doesn't expose its inner pointer mutably to the public? I would think that would get the job done, but I also haven't really done much Go since prior to generics being introduced

Otherwise, since pointers are frequently used to represent optional parameters, generics + sum types would get the job done; for that use case, it's one of two steps to solve the problem. I don't foresee Go adding sum types, though.

[suremarc]

Every type in Go has a zero value. The zero value for pointers is nil. So you can't do it with regular pointers, because users can always create an instance of the zero value.

[tialaramex]

This is one of those things which feels like just a small trade off against convenience for the language design, but then in practice it's a big headache you're stuck with in real systems.

It's basically mandating Rust's Default trait or the C++ default (no argument) constructor. In some places you can live with a Default but you wish there wasn't one. Default Gender = Male is... not great, but we can live with it, some natural languages work like this, and there are problems but they're not insurmountable. Default Date of Birth is... 1 January 1970 ? 1 January 1900? 0AD ? Also not a good idea but if you insist.

But in other places there just is no sane Default. So you're forced to create a dummy state, recapitulating the NULL problem but for a brand new type. Default file descriptor? No. OK, here's a "file descriptor" that's in a permanent error state, is that OK? All of my code will need to special case this, what a disaster.

[codetrotter]

> Default Gender = Male is... not great

    enum Gender {
        Unspecified,
        Male,
        Female,
        Other,
    }

    impl Default for Gender {
        default() -> Self {
            Self::Unspecified
        }
    }

or:

    enum Gender {
        Male,
        Female,
        Other,
    }

and use Option<Gender> instead of Gender directly, with Option::None here meaning the same that we would mean by Gender::Unspecified

[unrealhoang]

I think they are talking about the cons of Go allowing zero value. Rust doesn’t have that problem.

[andreyvit]

Default gender male not how this works in practice. Instead, you define an extra “invalid” value for almost every scalar type, so invalid would be 0, male 1 and female 2. Effectively this makes (almost) every scalar type nullable. It is surprisingly useful, though, and I definitely appreciate this tradeoff most of the time.

(Sometimes your domain type really does have a suitable natural default value, and you just make that the zero value.)

[stouset]

Great, now you’ve brought the pain of checking for nil to any consumer of this type too!

[tptacek]

This is a thread about Go, not about Rust. There is a bunch of interesting computer science in this post, and if interesting new computer science is a baby seal, Rust vs. Go discussions are hungry orcas.

[maccard]

I write a decent amount of go - this isn't a defence of the current situation.

> All of my code will need to special case this, what a disaster.

No, your code should handle the error state first and treat the value as invalid up until that point, e.g.

    foo, err := getVal()
    if err != nil {
        return
    }

    // foo can only be used now

It's infuriating that there's no compiler support to make this easier, but c'est la vie.

[leftyspook]

Man, if only over 30 odd years of PL research leading up to Go, somebody came up with a way to do it better.

[jasonhansel]

One answer would be to provide something like a GetPointer() method which, if the inner pointer is nil, creates a new struct of type T and returns a pointer to it.

[stouset]

Turns out worse isn’t better after all. Who could have guessed?

[Mawr]

You can make such a type and it works well in practice.

First we define the type, hiding the pointer/non-existent value:

    type Optional[Value any] struct {
        value  Value
        exists bool
    }

Then we expose it through a method:

    func (o Optional[Value]) Get() (Value, bool) {
        return o.value, o.exists
    }

Accessing the value then has to look like this:

    if value, ok := optional.Get(); ok {
        // value is valid
    }
    // value is invalid

This forces us to handle the nil/optional code path.

Here's a full implementation I wrote a while back: https://gist.github.com/MawrBF2/0a60da26f66b82ee87b98b03336e...

[tw061023]

Even if this would be possible, it won't be idiomatic.

[tw061023]

Without intention to offend. It's Golang, the language that famously ignored over 30 years of progress in language development for the sake of simplicity.

What answer do you expect?

[dang]

Hey, can you please not do programming language flamewar (or any flamewar) on HN? We're trying for something else here: https://news.ycombinator.com/newsguidelines.html.

Partly this is out of memory of the good/bad old newsgroup days where this kind of thing somehow worked ok, until it didn't, but it definitely doesn't work on the sort of forum that HN is. We'd like a better outcome than scorched earth for this place.