## Keyboard shortcuts

Press `←` or `→` to navigate between chapters

Press `S` or `/` to search in the book

Press `?` to show this help

Press `Esc` to hide this help

# Error code E0211

#### Note: this error code is no longer emitted by the compiler.

You used a function or type which doesn’t fit the requirements for where it was used. Erroneous code examples:

    #![feature(intrinsics)]
    #![allow(internal_features)]

    #[rustc_intrinsic]
    unsafe fn unreachable(); // error: intrinsic has wrong type

    // or:

    fn main() -> i32 { 0 }
    // error: main function expects type: `fn() {main}`: expected (), found i32

    // or:

    let x = 1u8;
    match x {
        0u8..=3i8 => (),
        // error: mismatched types in range: expected u8, found i8
        _ => ()
    }

    // or:

    use std::rc::Rc;
    struct Foo;

    impl Foo {
        fn x(self: Rc<Foo>) {}
        // error: mismatched self type: expected `Foo`: expected struct
        //        `Foo`, found struct `alloc::rc::Rc`
    }

For the first code example, please check the function definition. Example:

    #![allow(unused)]
    #![feature(intrinsics)]
    #![allow(internal_features)]

    fn main() {
    #[rustc_intrinsic]
    unsafe fn unreachable() -> !; // ok!
    }

The second case example is a bit particular: the main function must always have this definition:

    fn main();

They never take parameters and never return types.

For the third example, when you match, all patterns must have the same type as the type you’re matching on. Example:

    #![allow(unused)]
    fn main() {
    let x = 1u8;

    match x {
        0u8..=3u8 => (), // ok!
        _ => ()
    }
    }

And finally, for the last example, only `Box<Self>`, `&Self`, `Self`, or `&mut Self` work as explicit self parameters. Example:

    #![allow(unused)]
    fn main() {
    struct Foo;

    impl Foo {
        fn x(self: Box<Foo>) {} // ok!
    }
    }