If you wanted to list out cases without having to use `if`, `else if`, you'd idiomatically use match: fn calculate_tax(income: i32) -> i32 { match

If you wanted to list out cases without having to use `if`, `else if`, you'd idiomatically use match: fn calculate_tax(income: i32) -> i32 { match income { 0..10 => 0, 10..50 => 20, _ => 50, } } See this playground for a couple other alternatives using match too https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=1e7b3da5d8821ee99ee6d7f6936b0e21 https://play.rust-lang.org/?version=nightly&mode=debug&editi... As others explained, you do need a default case (either an 'else' in your if statement, or an exhaustive match), otherwise how would the expression typecheck? For a concrete example, if you use an 'if' only, you can have the following: let x = if income < 10 { 0 }; At that point, there's no way to statically know x's type. If income is >= 10, x is what? In order to convince the compiler x has a statically knowable type, the "if" expression need an else statement, or should be converted into a match that the compiler can prove is exhaustive.