patterns/idioms/rustdoc-init.md

# Easy doc initialization

## Description

If a struct takes significant effort to initialize, when writing docs it can be quicker to wrap your example with a 
function the struct as an argument.

## Motivation
Sometimes there is a struct with multiple or complicated parameters and several methods.
Each of these methods should have examples. 

For example:

```rust
struct Connection {
    name: String,
    stream: TcpStream,
}

impl Connection {
    /// Sends a request over the connection.
    /// # Example
    /// ```no_run
    /// # // Boilerplate are required to get an example working.
    /// # let stream = TcpStream::connect("127.0.0.1:34254");
    /// # let connection = Connection { name: "foo".to_owned(), stream };
    /// # let request = Request::new("RequestId", RequestType::Get, "payload");
    /// let response = connection.send_request(request);
    /// assert!(response.is_ok());
    /// ```
    fn send_request(&self, request: Request) -> Result<Status, SendErr> {
        //...
    }
        
    /// Oh no, all that boilerplate needs to be repeated here!
    fn check_status(&self) -> Status {
        // ...
    }
}
```

## Example
Instead of typing all of this boiler plate to create an `Connection` and `Request` it is easier to just create a wrapping dummy function which takes them as arguments:
```rust

struct Connection {
    name: String,
    stream: TcpStream,
    //...
}

impl Connection {
    /// Sends a request over the connection.
    /// # Example
    /// ```
    /// # fn call_send(connection: Connection, request: Request) {
    /// let result = connection.send_reqest();
    /// // do stuff with result.
    /// # }
    /// ```
    fn send_reqest(&self, request: Request) {
        //...
    }
}
```
## Advantages

This is much more concise and avoids repetitive code in examples.

## Disadvantages

Because the example is in a function, the code won't actually be tested. (Though it still will checked to make sure it compiles when running a `cargo test`)
So this pattern is most useful when you would need to add `no_run` anyway.

## Discussion

If assertions are not required this pattern works well. 

If they are, an alternative can be to create a public method to create a dummy instance which is annotated with `#[doc(hidden)]` (so that users won't see it).
Then this method can be called inside of Rustdocs because it is part of the crate's public API.