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
Here’s what you are trying to do, with a one liner:
fn get_links(mut link_nodes: Select) -> Vec<String> { link_nodes.retain(|node| node.value().attr("href").is_some()).into_iter().fold(Vec::new(), |links, node| links.push(link.value().attr("href").unwrap().to_string())) }edit: shorter and updated version:
fn get_links(mut link_nodes: Select) -> Vec<String> { link_nodes.into_iter().filter_map(|node| node.value().attr("href").map(|href| href.to_string())).collect() }The retain method is to get rid of all the nodes which don’t have a href attribute and the fold method after it is to extract the href out of the nodes and push them into the vector.
It might work or not, I’ve written this from my memory and I can’t exactly know what that Select is.
I also hope you begin reading The Book without half assing it.
You should use filter_map instead of the retain and later unwrapping and you don’t need a fold to build a Vec from an iterator, you can just use collect for that at the end.
here, it definitely is shorter, I’ll keep filter_map in mind, thanks:
fn get_links(mut link_nodes: Select) -> Vec<String> { link_nodes.into_iter().filter_map(|node| node.value().attr("href").map(|href| href.to_string())).collect() }