You used a function or type which doesn’t fit the requirements for where it was used. Erroneous code examples:
#![feature(intrinsics)]
extern "rust-intrinsic" {
fn size_of<T>(); // 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:
#![feature(intrinsics)]
extern "rust-intrinsic" {
fn size_of<T>() -> usize; // 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:
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:
struct Foo;
impl Foo {
fn x(self: Box<Foo>) {} // ok!
}