fn get_links(link_nodes: Select) -> Option<String> {
let mut rel_permalink: Option<String> = for node in link_nodes {
link = String::from(node.value().attr("href")?);
return Some(link);
};
Some(rel_permalink)
}
This is what I’m trying to do, and I’ve been stuck with this code for an hour, I simply don’t know how to put this function togheter… Essentially I would like to take some link_nodes and just return the link String, but I’m stuck in the use of Option with the ? operator…
Pheraps trying to write it with match would clear things out(?)
Also I come from JavaScript in which expressions do not have their own scope, meaning I’m having troubles to understand how to get out a variable from a for loop, should I initialize the rel_permalink variable as the for loop result?
This are the errors i get:
error[E0308]: mismatched types
--> src/main.rs:55:49
|
55 | let mut rel_permalink: Option<String> = for node in link_nodes {
| _________________________________________________^
56 | | link = String::from(node.value().attr("href")?);
57 | |
58 | | return Some(link);
59 | | };
| |_________^ expected `Option<String>`, found `()`
|
= note: expected enum `Option<String>`
found unit type `()`
note: the function expects a value to always be returned, but loops might run zero times
--> src/main.rs:55:49
|
55 | let mut rel_permalink: Option<String> = for node in link_nodes {
| ^^^^^^^^^^^^^^^^^^^^^^ this might have zero elements to iterate on
56 | link = String::from(node.value().attr("href")?);
| - if the loop doesn't execute, this value would never get returned
57 |
58 | return Some(link);
| ----------------- if the loop doesn't execute, this value would never get returned
= help: return a value for the case when the loop has zero elements to iterate on, or consider changing the return type to account for that possibility
@dontblink
enum OperativeSystem { Linux, Windows, Mac, Unrecognised, } fn find\_os(os: OperativeSystem) -\> String { match os { OperativeSystem::Linux =\> "This pc uses Linux".into(), OperativeSystem::Windows =\> "This pc uses Windows, unlucky you!".into(), OperativeSystem::Mac =\> "This pc uses Mac, I'm really sorry!".into(), \_ =\> "unrecognised".into(), } }If you want to return either a Boolean or a String you can introduce an enum
@dontblink e.g.
enum OsResponseType { Message { message: String }, Bool(bool), } fn find\_os(os: OperativeSystem) -\> OsResponseType { match os { OperativeSystem::Linux =\> OsResponseType::Message { message: "This pc uses Linux".into(), }, OperativeSystem::Windows =\> OsResponseType::Bool(false), OperativeSystem::Mac =\> OsResponseType::Bool(true), \_ =\> OsResponseType::Bool(false), } }Note the logic here is nonsense
@dontblink It feels like you should never
OsResponseType::Bool(true)so you could probably encode that in the enum just as the sameUnrecognisedenum OsResponseType { Message { message: String }, Unrecognised }Thank you so much, You are taking a lot of effort to answer my doubts and I really appreciate!
So essentially match can return different types, but of course I have to specify it in the function signature, wheter using an enum or other ways, this makes sense! This was a missing piece in my puzzle, I didn’t consider the fact that the match return here was the function return type as well, and i had encoded
-> Stringas return type.