[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.

[Kamq]

    type Gender int
    const (
        Unspecified Gender = iota
        Male
        Female
        Other
    )

Works the same way. Declaring an empty variable of the type Gender (var x Gender) results in unspecified.

[stouset]

…and now you need to check for nonsense values everywhere, instead of ever being able to know through the type system that you have a meaningful value.

It’s nil pointers all over again, but for your non-pointer types too! Default zero values are yet another own goal that ought to have been thrown away at the design stage.

[the_gipsy]

But it does not work. It looks like it would, with the indentation and iota keyword, but its just some variables that do not constrain the type. There will be incoming rogue values, from json or sql or something else.

    var g Gender // ok so far.
    if err := json.Unmarshal("99", &g); err != nil { panic(err) }
    // no error and g is Gender(99)!

Now you must validate, remember to validate, and do it in a thousand little steps in a thousand places.

Go is simple and gets you going fast... but later makes you stop and go back too much.

[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.

[maccard]

Given the choice between a (objectively) theoretically superior language like Haskell or Rust , and a language that prioritises developer ergonomics at the expense of PL research, I'll take the ergonomics thanks.

We have a 1MM line c++ codebase at work, a rust third party dependency, and a go service that's about as big as the rust dependency. Building the Rust app takes almost as long as the c++ app. Meanwhile, our go service is cloned, built, tested and deployed in under 5 minutes.

[mcronce]

Other than compiling a bit faster, what ergonomics does Go give you that Rust doesn't?

[pstuart]

And yet it's a productive language with significant adoption, go figure.

They made trade-offs and are conservative about refining the language; that cuts both ways but works well for a lot of people.

The Go team does seem to care about improving it and for many that use it, it keeps getting better. Perhaps it doesn't happen at the pace people want but they always have other options.

[stouset]

> And yet it's a productive language with significant adoption, go figure.

Perl was also a successful language with significant adoption. At least back then, we didn’t know any better.

In twenty years the industry will look back on golang as an avoidable mistake that hampered software development from maturing into an actual engineering discipline, for the false economy of making novice programmers quickly productive. I’m willing to put money on that belief, given sufficiently agreed upon definitions.

[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.