Maybe I am missing something here but as someone who is not an expert in go generics, I don't see any obvious "crimes" with the Option and Queue implementations.
I also could not find where the author explains their "crimes".
What I am missing here?
I also could not find where the author explains their "crimes".
What I am missing here?
The Option is just a good idea and sum types should have been in the language from the beginning to handle errors instead of product types. But that ship has sailed and sunk.
With the huge difference that Go’s pointers don’t statically require checking if they’re `null`.
Furthermore, you can add functor and monadic APIs to `Option` which provide completely safe (and somewhat efficient) usage patterns even if you build the option out of product types.
Though that isn’t the case here, an other interesting item is that you can build an option type out of non-pointer, thus avoiding the indirection and allocation (though hopefully unlike the C++ committee you don’t do it just so you have a pointer without an allocation)
>Furthermore, you can add functor and monadic APIs to `Option`
There's nothing preventing you from defining these functions directly on pointers, they'd be just as safe.
Whetger or not that’s the way you want to program is a whole different question, but you can get a level of safety from constructs like this you can’t get from a pointer.
Whether or not that’s the way you want to program is a whole different question, but you can get a level of safety from constructs like this you can’t get from a pointer.
It's consistent with the way Go's error handling works. Turns out it's not anywhere near as much of an issue as you might think. In practice you always notice that the function you're about to call returns an error and handle it.
> There's nothing preventing you from defining these functions directly on pointers, they'd be just as safe.
Pointers aren't Optionals. They happen to be nilable, yes, but their semantics are broader. A pointer can be used to avoid copying large structures around. How would you distinguish such a pointer vs one that's used as an Optional?
You choose if you want an exception. Map will only run if the optional contains a non-null value, so it won't throw. orElse will safely give you a value if the optional contains a null, so it won't throw either. The only time you throw is when you use orElseThrow, but that's in the name and you know what you're doing.
Ex.
Optional<Integer> x = Optional.ofNullable(null);
// This won't throw!
x.map(i -> i + 1);
// This won't throw either, and safeValue will *definitely* be an int!
int safeValue = x.orElse(5);
// This *will* throw, but you specify what to throw
x.orElseThrow(() -> new RuntimeException())
The latter. Java's Optionals are half-baked and don't provide as much safety as you'd think because it's easy for a `null` value to slip in. Notice how they used `Optional.ofNullable` — a common footgun is using `Optional.of(value)`, which throws a NullPointerException if `value` is null[1].
[1] https://docs.oracle.com/javase/8/docs/api/java/util/Optional...
Is it possible to church-encode these with Go generics?
As a casual Go user, it wasn't obvious whether those particular implementations were bad, whether the patterns themselves are a bad fit for the Go language, or whether there was just a better (more Go-like) way of doing things.
A better function to add to Optional[T] / *T would have been Map:
func Map[T any, V any] (o *T, foo func (T) V) *V {
if o == nil {
return nil
}
v := foo(*o)
return &v
}
func Map[T any, V any] (o Optional[T], foo func (T) V) Optional[V] {
if o.IsNone() {
return Optional[V]{}
}
return Optional[V]{foo(o.Yank())}
}