Common Rust Lifetime Misconceptions (2020)

@lysdexic@programming.dev · 8 months ago

Common Rust Lifetime Misconceptions (2020)

@robinm@programming.dev · 8 months ago

That’s a very nicecly written article.

Just a quick question, isn’t point 8 outdated (misconctption: “Rust borrow checker does adanced liftime analysis”) due to the introduction NLL (no lexical lifetime) in Rust 2018?

@hairyballs@programming.dev · edit-2 8 months ago

There are still obvious things the BC cannot get. For example:

struct Foo;

impl Foo {
    fn num(&amp;mut self) -> usize { 0 }
    fn index(&amp;mut self, _i: usize) { }
}

let foo = Foo;
foo.index(foo.num()); //error

@sirdorius@programming.dev · edit-2 8 months ago

This looks like a pretty easy fix that the compiler could do by extracting the argument to a temp variable to improve the syntax of the language.

@KillTheMule@programming.dev · edit-2 8 months ago

Note that when you change num to take &self instead, this works out (you also need to mark foo as mutable, of course).

@hairyballs@programming.dev · 8 months ago

It’s a toy example. In that case, the solution is to assign the expression to a variable to compute its result upfront.