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.
Specifically for this code, it's likely you should use f64::signum:
let r = 42.42_f64;
let sgn_r = r.signum();
来源：https://stackoverflow.com/questions/45092638/how-can-i-port-c-code-that-uses-the-ternary-operator-to-rust