Rust conditionals
if statement
if num < 5 { // .. } else if { // .. } else { // .. }
assign if
let weather = if season == "fall" { "lovely" } else { "fine I guess" } // ternary operator
match
Basics
Like a switch statement,
where compiler ensures that all possible options in datatype's range are handled,
that ensures the output type is the same for all branches (panic!()/break/return
also allowed).Especially useful for enums.
In the following case, if
_
was omitted
you'd need to ensure the full range of possible i32 numbers were supported!.// if num is '1', returns 'a' // if num is >2, returns 'c' let result = match num { 1 => "a", 2 => "b", _ => "c", // anything other than 1 or 2 }You can match multiple values
let result = match num { 1 | 3 | 5 => "one three or five", _ => "something else" }Matching Enums
When matching a parametrized enum, you can access the tuple/struct/value that is bound to it
enum Pet { Cat(String, u8), Dog{name: String, age: u8}, Lizard(u8), } let pet = Pet::Lizard(5); match pet { Pet::Cat(name, age) => { format!("cat, name={}, age={}", name, age) }, Pet::Dog(dog) => { format!("dog, name={dog.name}, age={dog.age}") }, Pet::Lizard(age) => { format!("lizard, age={}", age) } }Matching Option
Option is just an enum, generally if you don't have a specific behaviour for
None
,
you return a newNone
in that branch.
However this an opportunity to fail if it is an appropriate location for it.match some_value { Some(x) => "you received a value!", None => None, }Matching Ranges
match val { i32::MIN..0 => "less than zero", 0..5 => "is zero to five", 5..i32::MAX => "is over five", }use std::cmp::Ordering; // todo
if let
if let is essentially a one-branch
match
,
only caring about the value if it is non-none.
ifmy_value
isNone
, then it returnsNone
and the block does not run.it does not take advantage of exhaustiveness checks.
if let Some(x) = my_value { println!("The value {} was bound!!", x); }