try! won't compile mismatched types - macros

Question

Why doesn't this Rust code compile?
use std::fs;
use std::io;
use std::path::Path;
fn do_job(path: &Path) -> io::Result<()> {
let mut files: Vec<&Path> = Vec::new();
for entry in try!(fs::read_dir(path)) {
entry = try!(entry);
}
}
it's very similar to code in the docs.
compile error:
<std macros>:3:43: 3:46 error: mismatched types:
expected `core::result::Result<std::fs::DirEntry, std::io::error::Error>`,
found `std::fs::DirEntry`
(expected enum `core::result::Result`,
found struct `std::fs::DirEntry`) [E0308]
<std macros>:3 $ crate:: result:: Result:: Ok ( val ) => val , $ crate:: result:: Result::
^~~
src/main.rs:13:17: 13:28 note: in this expansion of try! (defined in <std macros>)
<std macros>:3:43: 3:46 help: run `rustc --explain E0308` to see a detailed explanation
src/main.rs:12:5: 14:6 error: mismatched types:
expected `core::result::Result<(), std::io::error::Error>`,
found `()`
(expected enum `core::result::Result`,
found ()) [E0308]
src/main.rs:12 for entry in try!(fs::read_dir(path)) {
src/main.rs:13 entry = try!(entry);
src/main.rs:14 }
src/main.rs:12:5: 14:6 help: run `rustc --explain E0308` to see a detailed explanation

Answer 1

It looks like you want a new binding for each directory entry in your loop:
for entry in fs::read_dir(path)? {
let entry = entry?;
}
this new binding will shadow the one introduced in the for expression.
The type of entry introduced by the loop is Result<DirEntry> which you are trying to unwrap using ? (formerly try!). However you are attempting to assign the resulting DirEntry to a binding with type Result<DirEntry>, hence the error.
The second error indicates that the return value from your function does not match the declared type of io::Result<()>. You can simply return Ok(()):
fn do_job(path: &Path) -> io::Result<()> {
let mut files: Vec<&Path> = Vec::new();
for entry in fs::read_dir(path)? {
let entry = entry?;
//process entry
}
Ok(())
}