Nitpicking: assignment is an expression that returns () in Rust, meaning `foo(a = 1, a)` is valid if foo has a signature like `fn foo(x: (), y: i32)`. However,

Nitpicking: assignment is an expression that returns () in Rust, meaning `foo(a = 1, a)` is valid if foo has a signature like `fn foo(x: (), y: i32)`. However, arguments are (mostly) defined to be evaluated from left to right.