No method/field name found - rust

Question

I'm trying to apply some OOP but I'm facing a problem.
use std::io::Read;
struct Source {
look: char
}
impl Source {
fn new() {
Source {look: '\0'};
}
fn get_char(&mut self) {
self.look = 'a';
}
}
fn main() {
let src = Source::new();
src.get_char();
println!("{}", src.look);
}
Compiler reports these errors, for src.get_char();:
error: no method named get_char found for type () in the current
scope
and for println!("{}", src.look);:
attempted access of field look on type (), but no field with that
name was found
I can't find out what I've missed.

Answer 1

Source::new has no return type specified, and thus returns () (the empty tuple, also called unit).
As a result, src has type (), which does not have a get_char method, which is what the error message is telling you.
So, first things first, let's set a proper signature for new: fn new() -> Source. Now we get:
error: not all control paths return a value [E0269]
fn new() -> Source {
Source {look: '\0'};
}
This is caused because Rust is an expression language, nearly everything is an expression, unless a semicolon is used to transform the expression into a statement. You can write new either:
fn new() -> Source {
return Source { look: '\0' };
}
Or:
fn new() -> Source {
Source { look: '\0' } // look Ma, no semi-colon!
}
The latter being the more idiomatic in Rust.
So, let's do that, now we get:
error: cannot borrow immutable local variable `src` as mutable
src.get_char();
^~~
Which is because src is declared immutable (the default), for it to be mutable you need to use let mut src.
And now it all works!
Final code:
use std::io::Read;
struct Source {
look: char
}
impl Source {
fn new() -> Source {
Source {look: '\0'}
}
fn get_char(&mut self) {
self.look = 'a';
}
}
fn main() {
let mut src = Source::new();
src.get_char();
println!("{}", src.look);
}
Note: there is a warning because std::io::Read is unused, but I assume you plan to use it.