error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32` --> $DIR/fn-trait.rs:20:16 | LL | require_fn(f as unsafe fn() -> i32); | ---------- ^^^^^^^^^^^^^^^^^^^^^^^ call the function in a closure: `|| unsafe { /* code */ }` | | | required by a bound introduced by this call | = help: the trait `Fn<()>` is not implemented for `unsafe fn() -> i32` = note: unsafe function cannot be called generically without an unsafe block = note: wrap the `unsafe fn() -> i32` in a closure with no arguments: `|| { /* code */ }` note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:23 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^^^^^^^^^ required by this bound in `require_fn` error[E0271]: type mismatch resolving ` i32 as FnOnce<()>>::Output == i32` --> $DIR/fn-trait.rs:20:16 | LL | require_fn(f as unsafe fn() -> i32); | ---------- ^^^^^^^^^^^^^^^^^^^^^^^ types differ | | | required by a bound introduced by this call | note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:31 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^ required by this bound in `require_fn` error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32 {g}` --> $DIR/fn-trait.rs:23:16 | LL | require_fn(g); | ---------- ^ expected an `Fn()` closure, found `extern "C" fn() -> i32 {g}` | | | required by a bound introduced by this call | = help: the trait `Fn<()>` is not implemented for fn item `extern "C" fn() -> i32 {g}` = note: wrap the `extern "C" fn() -> i32 {g}` in a closure with no arguments: `|| { /* code */ }` note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:23 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^^^^^^^^^ required by this bound in `require_fn` error[E0271]: type mismatch resolving ` i32 {g} as FnOnce<()>>::Output == i32` --> $DIR/fn-trait.rs:23:16 | LL | require_fn(g); | ---------- ^ types differ | | | required by a bound introduced by this call | note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:31 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^ required by this bound in `require_fn` error[E0277]: expected a `Fn()` closure, found `extern "C" fn() -> i32` --> $DIR/fn-trait.rs:26:16 | LL | require_fn(g as extern "C" fn() -> i32); | ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected an `Fn()` closure, found `extern "C" fn() -> i32` | | | required by a bound introduced by this call | = help: the trait `Fn<()>` is not implemented for `extern "C" fn() -> i32` = note: wrap the `extern "C" fn() -> i32` in a closure with no arguments: `|| { /* code */ }` note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:23 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^^^^^^^^^ required by this bound in `require_fn` error[E0271]: type mismatch resolving ` i32 as FnOnce<()>>::Output == i32` --> $DIR/fn-trait.rs:26:16 | LL | require_fn(g as extern "C" fn() -> i32); | ---------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ | | | required by a bound introduced by this call | note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:31 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^ required by this bound in `require_fn` error[E0277]: expected a `Fn()` closure, found `unsafe fn() -> i32 {h}` --> $DIR/fn-trait.rs:29:16 | LL | require_fn(h); | ---------- ^ call the function in a closure: `|| unsafe { /* code */ }` | | | required by a bound introduced by this call | = help: the trait `Fn<()>` is not implemented for fn item `unsafe fn() -> i32 {h}` = note: unsafe function cannot be called generically without an unsafe block = note: wrap the `unsafe fn() -> i32 {h}` in a closure with no arguments: `|| { /* code */ }` note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:23 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^^^^^^^^^ required by this bound in `require_fn` error[E0271]: type mismatch resolving ` i32 {h} as FnOnce<()>>::Output == i32` --> $DIR/fn-trait.rs:29:16 | LL | require_fn(h); | ---------- ^ types differ | | | required by a bound introduced by this call | note: required by a bound in `require_fn` --> $DIR/fn-trait.rs:3:31 | LL | fn require_fn(_: impl Fn() -> i32) {} | ^^^ required by this bound in `require_fn` error: aborting due to 8 previous errors Some errors have detailed explanations: E0271, E0277. For more information about an error, try `rustc --explain E0271`.