Rust

Trick question: what is the return type of a function with body

{
   return || true
}

Let’s try a more difficult one with closures. What’s wrong with this closure

let closure = |x: &str| x;

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Very warm! Why does this work though?

fn foo(s: &str) -> &str { s }

You would need to specify a lifetime since you’re returning a borrowed reference. I don’t remember right now if you can annotate lifetimes in closures 😅 but you could do:

let closure = |x: &str| x.to_owned();

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probably something ownership/lifetime related?

Good question, but no, the former assigns the value of x to the variable named closure (whatever x is), while the latter assign the specific closure to the variable where x is an input parameter.

In fact you could remove the “let closure =“ part and the problem would persist I just wanted to make it easier to read

Isn't "let closure = x;"  doing the same thing as "let closure = |x: &str| x;"?