hairyballs comments on Common Rust Lifetime Misconceptions (2020)

[–] hairyballs@programming.dev 1 point 2 years ago* (2 children)

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

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[–] sirdorius@programming.dev 2 points 2 years 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.

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[–] KillTheMule@programming.dev 1 point 2 years ago* (1 child)

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

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[–] hairyballs@programming.dev 1 point 2 years ago

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

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