fork(1) download

use std::collections::HashMap;
use std::io::{self, Error, ErrorKind};
 
pub struct A {
    x: i32,
}
 
pub struct B {
    a: u32,
}
 
impl std::hash::Hash for A {
    fn hash<H>(&self, state: &mut H) -> Result<(), io::Error>
    where
        H: std::hash::Hasher,
    {
        if self.x == 5 {
          return Error::new(ErrorKind::Other, "oh no!");
        }
        state.write_i32(self.x);
        state.finish();
    }
}
 
impl PartialEq for A {
    fn eq(&self, other: &A) -> bool {
        self.x == other.x
    }
}
 
impl Eq for A {}
 
fn main() {
    let mut map = HashMap::new();
    map.insert(
        A {
            x: 10,
        },
        B { a: 1 },
    );
}

error[E0053]: method `hash` has an incompatible type for trait
  --> prog.rs:13:41
   |
13 |     fn hash<H>(&self, state: &mut H) -> Result<(), io::Error>
   |                                         ^^^^^^^^^^^^^^^^^^^^^
   |                                         |
   |                                         expected `()`, found enum `Result`
   |                                         help: change the output type to match the trait: `()`
   |
   = note: expected fn pointer `fn(&A, &mut H)`
              found fn pointer `fn(&A, &mut H) -> Result<(), std::io::Error>`

error[E0308]: mismatched types
  --> prog.rs:18:18
   |
13 |     fn hash<H>(&self, state: &mut H) -> Result<(), io::Error>
   |                                         --------------------- expected `Result<(), std::io::Error>` because of return type
...
18 |           return Error::new(ErrorKind::Other, "oh no!");
   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                  |
   |                  expected enum `Result`, found struct `std::io::Error`
   |                  help: try using a variant of the expected enum: `Err(Error::new(ErrorKind::Other, "oh no!"))`
   |
   = note: expected enum `Result<(), std::io::Error>`
            found struct `std::io::Error`

error[E0308]: mismatched types
  --> prog.rs:13:41
   |
13 |     fn hash<H>(&self, state: &mut H) -> Result<(), io::Error>
   |        ----                             ^^^^^^^^^^^^^^^^^^^^^ expected enum `Result`, found `()`
   |        |
   |        implicitly returns `()` as its body has no tail or `return` expression
   |
   = note:   expected enum `Result<(), std::io::Error>`
           found unit type `()`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0053, E0308.
For more information about an error, try `rustc --explain E0053`.

Standard output is empty