Warning

This post was published 113 days ago. The information described in this article may have changed.

Info

This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Making two function types implement a trait?

Why are these to impls "conflicting", and how do I get around this? What I'm trying to say seems logical: I have this trait called ClickListener and things that are Fn() or Fn(Event) implement it. Is it complaining because it's possible to have a type that implements both those traits, so then it wouldn't know which impl to use between 1 and 2 below? Maybe there is a way to tell it which one takes priority in that case?

playground link

#![allow(dead_code)]

#[derive(Debug)]
struct Event {
    foo: i32,
}
trait ClickListener {
    fn on_click(&self, event: Event);
}

// impl #1
impl<F: Fn(Event)> ClickListener for F {
    fn on_click(&self, event: Event) {
        (self)(event)
    }
}
// impl #2
impl<F: Fn()> ClickListener for F {
    fn on_click(&self, _event: Event) {
        (self)()
    }
}

struct ButtonBuilder {
    text: String,
    on_click: Option<Box<dyn ClickListener>>,
}

impl ButtonBuilder {
    fn text<S: Into<String>>(mut self, s: S) -> Self {
        self.text = s.into();
        self
    }
    fn on_click<F: ClickListener + 'static>(mut self, f: F) -> Self {
        self.on_click = Some(Box::new(f));
        self
    }
    fn new() -> Self {
        ButtonBuilder {
            text: "".to_string(),
            on_click: None,
        }
    }
}

fn main() {
    let _b = ButtonBuilder::new()
        .on_click(|e: Event| println!("click! e = {:?}", e));
    let _b = ButtonBuilder::new()
        .on_click(|| println!("click!"));
}

Error:

Compiling playground v0.0.1 (/playground)
error[E0119]: conflicting implementations of trait `ClickListener`
  --> src/main.rs:18:1
   |
12 | impl<F: Fn(Event)> ClickListener for F {
   | -------------------------------------- first implementation here
...
18 | impl<F: Fn()> ClickListener for F {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation

3 posts - 2 participants

Read full topic

🏷️ rust_feed