How can I port C++ code that uses the ternary operator to Rust?

How can I port this C++ code to Rust:

auto sgnR = (R >= 0.) ? 1. : -1.; 

I have seen some examples with the match keyword, but I don't understand how it works.

2 Answers

Rust does not have the ternary operator because it's not needed. Everything evaluates to some value, and if / else statements are no exception:

let r = 42.42; let sgn_r = if r >= 0. { 1. } else { -1. }; 

You'll note that I've also changed your variable names to be idiomatic Rust. Identifiers use snake_case.

Do not be confused by the ? operator that Rust does have. This is called the "try operator" and is used to propagate errors.

Specifically for this code, it's likely you should use f64::signum:

let r = 42.42_f64; let sgn_r = r.signum(); 

As of Rust 1.50, you can use bool::then to accomplish the same thing:

let sgn_r = (r >= 0).then(|| 1).unwrap_or(-1); 

Note that it is generally better to use a regular if/else statement for readability reasons, but bool::then is an alternative that may be nicer in certain circumstances.