error[E0005]: refutable pattern in local binding: `None` not covered --> $DIR/E0005.rs:3:9 | LL | let Some(y) = x; | ^^^^^^^ pattern `None` not covered | = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html note: `Option` defined here --> $SRC_DIR/core/src/option.rs:LL:COL | LL | pub enum Option { | ------------------ ... LL | None, | ^^^^ not covered = note: the matched value is of type `Option` help: you might want to use `if let` to ignore the variant that isn't matched | LL | let y = if let Some(y) = x { y } else { todo!() }; | ++++++++++ ++++++++++++++++++++++ help: alternatively, you might want to use let else to handle the variant that isn't matched | LL | let Some(y) = x else { todo!() }; | ++++++++++++++++ error: aborting due to previous error For more information about this error, try `rustc --explain E0005`.