Expected () but found a struct [duplicate] - rust

Question

This question already has an answer here:
Why does removing return give me an error: expected type `()` but found type
(1 answer)
Closed 6 years ago.
I have a world object:
use rand::{thread_rng, Rng};
use super::world::World;
pub struct Worlds {
worlds: Vec<World>
}
impl Worlds {
pub fn new(world: Vec<World>) -> Worlds {
Worlds { worlds: world }
}
pub fn get_random_world(&self) -> World {
let mut rng = thread_rng();
if self.worlds.len() > 0 {
let world_index: usize = rng.gen_range(0, self.worlds.len());
self.worlds[world_index]
}
self.worlds[0]
}
}
The structure Worlds takes a vector of structures called World (I can post that code if you need it).
get_random_world is supposed to return a World structure, and does with self.worlds[world_index], but apparently it expects a ().
I'm lost; I told it what to return, it returns that but it expects something different?
|
20 | self.worlds[world_index]
| ^^^^^^^^^^^^^^^^^^^^^^^^ expected (), found struct `game::world::world::World`
|
= note: expected type `()`
= note: found type `game::world::world::World`
I'm not sure what to do at this point.

Answer 1

Your if block doesn't return anything.. flow will fall through here:
if self.worlds.len() > 0 {
let world_index: usize = rng.gen_range(0, self.worlds.len());
self.worlds[world_index]
} // <--- ... this drops down
self.worlds[0]
Here is a simple reproduction of your issue: Playground link
There are two ways you can fix this. First, you can explicitly return in the conditional (View it on the playground):
if self.worlds.len() > 0 {
let world_index: usize = rng.gen_range(0, self.worlds.len());
return self.worlds[world_index]; // Explicitly return out of here
}
self.worlds[0]
The more "idiomatic" approach I guess would be to add an else block, so that the value the conditional evaluates to is actually what the function returns (View it on the playground):
if self.worlds.len() > 0 {
let world_index: usize = rng.gen_range(0, self.worlds.len());
self.worlds[world_index]
} else {
self.worlds[0]
}
Now, no matter what logical branch the code takes, the expression that results will be returned from the function.