error[E0594]: cannot assign to `n`, as it is not declared as mutable --> $DIR/unboxed-closures-mutate-upvar.rs:15:9 | LL | let n = 0; | - help: consider changing this to be mutable: `mut n` LL | let mut f = to_fn_mut(|| { LL | n += 1; | ^^^^^^ cannot assign error[E0594]: cannot assign to `n`, as it is not declared as mutable --> $DIR/unboxed-closures-mutate-upvar.rs:32:9 | LL | let n = 0; | - help: consider changing this to be mutable: `mut n` ... LL | n += 1; | ^^^^^^ cannot assign error[E0594]: cannot assign to `n`, as it is not declared as mutable --> $DIR/unboxed-closures-mutate-upvar.rs:46:9 | LL | let n = 0; | - help: consider changing this to be mutable: `mut n` LL | let mut f = to_fn(move || { LL | n += 1; | ^^^^^^ cannot assign error[E0594]: cannot assign to `n`, as it is a captured variable in a `Fn` closure --> $DIR/unboxed-closures-mutate-upvar.rs:53:9 | LL | fn to_fn>(f: F) -> F { f } | - change this to accept `FnMut` instead of `Fn` ... LL | let mut f = to_fn(move || { | ----- ------- in this closure | | | expects `Fn` instead of `FnMut` LL | n += 1; | ^^^^^^ cannot assign error: aborting due to 4 previous errors For more information about this error, try `rustc --explain E0594`.