Rust if let

The if let syntax lets you combine if and let into a less verbose way to handle values that match one pattern while ignoring the rest.

The syntax if let takes a pattern and an expression separated by an equal sign. It works the same way as a match, where the expression is given to the match and the pattern is its first arm.

// Instead of
let config_max = Some(3u8);
match config_max {
	Some(max) => println!("The maximum is configured to be {}", max),
	_ => (),
}
 
// We can write this
let config_max = Some(3u8);
if let Some(max) = config_max {
	println!("The maximum is configured to be {}", max);
}

You can think of if let as syntax sugar for a match that runs code when the value matches one pattern and then ignores all other values.

We can include an else with an if let. The block of code that goes with the else is the same as the block of code that would go with the _ case in the match expression that is equivalent to the if let and else.

// Instaed of
let mut count = 0;
match coin {
	Coin::Quarter(state) => println!("State quarter from {:?}!", state),
	_ => count += 1,
}
 
// We can write this
let mut count = 0;
if let Coin::Quarter(state) = coin {
	println!("State quarter from {:?}!", state);
} else {
	count += 1;
}