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## get_document_id
### Instructions
Create the following structures which will help you get the `document_id` of the document you need.
- `OfficeOne`: `next_office` as type `Result<OfficeTwo, ErrorOffice>`.
- `OfficeTwo`: `next_office` as type `Result<OfficeThree, ErrorOffice>`.
- `OfficeThree`: `next_office` as type `Result<OfficeFour, ErrorOffice>`.
- `OfficeFour`: `document_id` as type `Result<u32, ErrorOffice>`.
`ErrorOffice` is an `enum` with `OfficeClosed(u32)`, `OfficeNotFound(u32)` or `OfficeFull(u32)`.
The `u32` is the `id` of the office generating the error.
Beside the structures, you must create a **function** named `get_document_id`, and associate it to the `OfficeOne` structure.
This **function** should return the `Result` value in the `OfficeFour` structure or the first `Err` it finds in the chain.
### Expected Function and structures
```rust
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum ErrorOffice {
OfficeClose(u32),
OfficeNotFound(u32),
OfficeFull(u32),
}
#[derive(PartialEq, Eq, Clone, Copy)]
pub struct OfficeOne {
pub next_office: Result<OfficeTwo, ErrorOffice>,
}
#[derive(PartialEq, Eq, Clone, Copy)]
pub struct OfficeTwo {
pub next_office: Result<OfficeThree, ErrorOffice>,
}
#[derive(PartialEq, Eq, Clone, Copy)]
pub struct OfficeThree {
pub next_office: Result<OfficeFour, ErrorOffice>,
}
#[derive(PartialEq, Eq, Clone, Copy)]
pub struct OfficeFour {
pub document_id: Result<u32, ErrorOffice>,
}
impl OfficeOne {
pub fn get_document_id(&self) -> Result<u32, ErrorOffice> {}
}
```
### Usage
Here is a program to test your function.
```rust
use get_document_id::*;
fn main() {
let office_ok = OfficeOne {
next_office: Ok(OfficeTwo {
next_office: Ok(OfficeThree {
next_office: Ok(OfficeFour {
document_id: Ok(13),
}),
}),
}),
};
let office_closed = {
OfficeOne {
next_office: Ok(OfficeTwo {
next_office: Err(ErrorOffice::OfficeClose(23)),
}),
}
};
match office_ok.get_document_id() {
Ok(id) => println!("Found a document with id {}", id),
Err(err) => println!("Error: {:?}", err),
};
match office_closed.get_document_id() {
Ok(id) => println!("Found a document with id {}", id),
Err(err) => println!("Error: {:?}", err),
};
}
```
And its output:
```console
$ cargo run
Found a document with id 13
Error: OfficeClose(23)
$
```