### What it does

Checks for calls to `iter`, `iter_mut` or `into_iter` on collections containing a single item

### Why is this bad?

It is simpler to use the once function from the standard library:

### Example

```
let a = [123].iter();
let b = Some(123).into_iter();
```
Use instead:
```
use std::iter;
let a = iter::once(&123);
let b = iter::once(123);
```

### Known problems

The type of the resulting iterator might become incompatible with its usage