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What are some mind blowing Rust tricks? (self.rust)

submitted 1 month ago* (last edited 1 month ago) by little_ferris to c/rust

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If we were to create a Rust version of this page for Haskell, what cool programming techniques would you add to it?

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[–] [email protected] 12 points 1 month ago (8 children)

Something i didnt know for a long time (even though its mentioned in the book pretty sure) is that enum discriminants work like functions

#[derive(Debug, PartialEq, Eq)]
enum Foo {
    Bar(i32),
}

let x: Vec<_> = [1, 2, 3]
    .into_iter()
    .map(Foo::Bar)
    .collect();
assert_eq!(
    x,
    vec![Foo::Bar(1), Foo::Bar(2), Foo::Bar(3)]
);

Not too crazy but its something that blew my mind when i first saw it

[–] little_ferris 2 points 1 month ago (1 children)

Yea it's like when we writeSome(2). It's not a function call but a variant of the Option enum.

[–] [email protected] 3 points 1 month ago (2 children)

Enum constructors are functions, this typechecks:

fn foo<T>() {
    let f: fn(T) -> Option<T> = Some;
}

I was a bit apprehensive because rust has like a gazillion different function types but here it seems to work like just any other language with a HM type system.

[–] little_ferris 2 points 1 month ago

Woah. That's quite interesting. I didn't know that.

[–] [email protected] 1 points 1 month ago

I was a bit apprehensive because rust has like a gazillion different function types but here it seems to work like just any other language with a HM type system.

The fn(T)->R syntax works for functions without associated data, it discards details of the implementation and works like function pointers in C. This allows them to be copy and 'static.

The other function types can have data with them and have more type information at compile time which allows them to be inlined.
These functions each have their own unwritable type that implements the function traits (Fn(T)->R, FnMut(T)->R and FnOnce(T)->R) depending on their enclosed data.

I hope I remembered everything right from this video by Jon Gjengset.

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