Mastering Rust - Second Edition

Common combinators

Let's look at some of the useful combinators that are available for both the Option and Result types:

map: This method allows you to transform the success value, T, to another value, U. The following is the type signature of map for the Option type:

pub fn map<U, F>(self, f: F) -> Option<U>where F: FnOnce(T) -> U {    match self {        Some(x) => Some(f(x)),        None => None,    }}

The following is the signature for the Result type:

pub fn map<U, F>(self, f: F) -> Option<U>where F: FnOnce(T) -> U {    match self {        Ok(t) => Ok(f(t)),        Err(e) => Err(e)    }}

This method's type signature can be read as follows: map is a generic method over U and F, and takes self by value. It then takes a parameter, f, of type F and returns an Option<U>, where ...