Ignoring some field of struct when using derive

help
1

In this MWE (link to rust-playground), I use a priority queue to store Task. I want them to be sorted by when_to_execute (which is the time, no other field matter). Since I am lazy, I just used the derive attribute to implement required traits.

use chrono::prelude::*;
use chrono::Utc;

use std::collections::BinaryHeap;

#[derive(Debug, PartialOrd, Ord, PartialEq, Eq)]
struct Task {
    when_to_execute: DateTime<Utc>,
    label : String,
    // foo : &Foo   // Foo doesn't have required traits such as Eq etc.
}


fn main() {
    let mut jm : BinaryHeap<Task> = BinaryHeap::new();
    jm.push( Task{ label : "A".to_string(), when_to_execute: Utc::now()});
    jm.push( Task{ label : "B".to_string(), when_to_execute: Utc::now()});
    jm.push( Task{ label : "C".to_string(), when_to_execute: Utc::now()});
    
    while ! jm.is_empty() {
        println!("{:?}", jm.pop());
    }
}

Output:

Some(Task { when_to_execute: 2021-12-27T15:15:58.751650790Z, label: "C" })
Some(Task { when_to_execute: 2021-12-27T15:15:58.751648633Z, label: "B" })
Some(Task { when_to_execute: 2021-12-27T15:15:58.751641679Z, label: "A" })

This is as I expected. Now, If I uncomment foo, the code will not compile because Foo doesn't have required traits to be in priority queue.

Is there a way I can resolve this issue without adding Eq etc. traits to Foo? Maybe some sort of macro that can ignore field foo when Eq is implemented by derive?

Update

  1. Looks like there is no simple solution: rust - Exclude field when deriving PartialEq - Stack Overflow
2

No, unless the macro includes special support for it, this isn't possible.

1 Like
3

Thanks @alice. I ended up using Overview - Derivative .

4

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