For some use cases, match
is awkward. For example:
// Make `optional` of type `Option<i32>`
let optional = Some(7);
match optional {
Some(i) => {
println!("This is a really long string and `{:?}`", i);
// ^ Needed 2 indentations just so we could destructure
// `i` from the option.
},
_ => {},
// ^ Required because `match` is exhaustive. Doesn't it seem
// like wasted space?
};
if let
is cleaner for this use case and in addition allows various
failure options to be specified:
fn main() { // All have type `Option<i32>` let number = Some(7); let letter: Option<i32> = None; let emoticon: Option<i32> = None; // The `if let` construct reads: "if `let` destructures `number` into // `Some(i)`, evaluate the block (`{}`). if let Some(i) = number { println!("Matched {:?}!", i); } // If you need to specify a failure, use an else: if let Some(i) = letter { println!("Matched {:?}!", i); } else { // Destructure failed. Change to the failure case. println!("Didn't match a number. Let's go with a letter!"); }; // Provide an altered failing condition. let i_like_letters = false; if let Some(i) = emoticon { println!("Matched {:?}!", i); // Destructure failed. Evaluate an `else if` condition to see if the // alternate failure branch should be taken: } else if i_like_letters { println!("Didn't match a number. Let's go with a letter!"); } else { // The condition evaluated false. This branch is the default: println!("I don't like letters. Let's go with an emoticon :)!"); }; }