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fn with_closure<F, A, B>(_: F) where F: FnOnce(A, B) { } fn a() { // Type of `y` is unconstrained. with_closure(|x: u32, y| {}); //~ ERROR E0282 } fn b() { with_closure(|x: u32, y: u32| {}); // OK } fn c() { with_closure(|x: u32, y: u32| {}); // OK } fn main() { }