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How to define / edit a struct istance field with a method? (feddit.it)

submitted 2 days ago* (last edited 2 days ago) by dontblink@feddit.it to c/rust@lemmy.ml

6 comments fedilink hide all child comments

Let's say I have a struct Event which implements the method permalink:

struct Event {
    base_url: String,
    rel_permalink: String,
    permalink: String,
    title: String,
}

impl Event {
    fn permalink(&self) -> String {
        let permalink = format!("{}{}", self.base_url, self.rel_permalink);
        permalink
    }
}

The method takes 2 fields of the struct and the target would be to return the definition of another field.

Later I instantiate an event1: Event:

let event1 = Event {
                base_url: base_url,
                rel_permalink: rel_permalink.to_string(),
                title: node.value().name().to_string(),
                permalink = permalink(),
            };

Essentially I would like the field permalink to be the value returned by the method permalink, is something like this possible, is this correct? I couldn't find something similar in the docs..

Pheraps using an associated function as constructor would be a better way to handle a similar situation?

Thank you so much!

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[–] Ephera@lemmy.ml 2 points 2 days ago* (last edited 2 days ago) (2 children)

Hmm, yeah, I'd use a constructor method:

impl Event {
    pub fn new(base_url: String, rel_permalink: String, title: String) -> Self {
        let permalink = format!("{}{}", self.base_url, self.rel_permalink);

        Self {
                base_url,
                rel_permalink,
                title,
                permalink,
         };
    }

    // ...
}

Then you'd instantiate it like so:

let title = node.value().name().to_string();
let event = Event::new(base_url, rel_permalink.to_string(), title);

[–] GissaMittJobb@lemmy.ml 1 points 2 days ago* (last edited 2 days ago) (1 children)

~~Is it really valid to call permalink() in that context, since it requires &self? There's no self in that context afaik. Can't test it now but it looks suspicious~~

EDIT: Invalid since the comment was updated

[–] Ephera@lemmy.ml 2 points 2 days ago

Sorry, I posted the comment, then realized that problem. 😅