How can I port C++ code that uses the ternary oper

问题:

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.

回答1:

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.

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

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