How do I conditionally execute code only when an Option is None?

Question

I don't want to take action if the function returns a value in the optional; how do I test the None case only? This code works, but it looks horrible.

let v = ffunc(); match v {   None => { callproc() },    Some(x) => {  } } 

In C, I can write:

int x = ffunc(); if ( !x ) { callproc() }  

Answer 1

To check if an Option is None you can either use Option::is_none or use the if let syntax.

For example:

let x = ffunc();  if let None = x {     println!("x is None") } 

Or using the Option::is_none function:

let x = ffunc();  if x.is_none() {     println!("x is None") } 

Answer 2

If you are not interested in the value, just use

if v.is_none() { ... }