Clash Royale CLAN TAG#URR8PPP

Why does serde_json::from_reader take ownership of the reader?

My code:

fn request_add<T>(request: &mut Request, collection_name: &'static str) -> Fallible<Fallible<String>>
where
T: serde::Serialize + serde::de::DeserializeOwned,

let add_dao = dao::MongoDao::new(collection_name);
let obj = serde_json::from_reader::<Body, T>(request.body)?; //cannot move out of borrowed content
Ok(add_dao.add(&obj))



I have a cannot move out of borrowed content error, because request is a reference, but why does serde_json::from_reader not use a mut reference? Why does it need ownership? And how can I fix it?

cannot move out of borrowed content

request

serde_json::from_reader

1 Answer
1

Because it's an API guideline:

R: Read

W: Write

The standard library contains these two impls:

impl<'a, R: Read + ?Sized> Read for &'a mut R /* ... */

impl<'a, W: Write + ?Sized> Write for &'a mut W /* ... */


That means any function that accepts R: Read or W: Write generic
parameters by value can be called with a mut reference if necessary.

R: Read

W: Write

mut

You either call Read::by_ref or just take a reference yourself:

Read::by_ref

serde_json::from_reader(&mut request.body)


serde_json::from_reader(request.body.by_ref())


See also:

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