Tracking issue for Option::contains and Result::contains

This is a tracking issue for Option::contains and Result::contains.

The implementations are as follows:

    pub fn contains(&self, x: &T) -> bool where T: PartialEq {
        match self {
            Some(y) => y == x,
            None => false,
        }
    }

    pub fn contains(&self, x: &T) -> bool where T: PartialEq {
        match self {
            Ok(y) => y == x,
            Err(_) => false,
        }
    }
``

Should we update the signatures to fn contains<U>(&self, x: &U) -> bool where T: PartialEq<U>?

@Mark-Simulacrum

@Mark-Simulacrum That seems like a good idea -- type inference should be driven by x in any case. Let's do that in the PR.

Looks like slice/Vec/VecDeque/LinkedList and possibly others have a contains method that could benefit in the same way.

@Mark-Simulacrum

@Mark-Simulacrum I didn't do that because I checked the collections first, and they were all invariant. Shall I change this for Option and Result only?

We usually can't change preexisting APIs due to inference breakage, but since this is new, we should be able to be general.

Are these functionally equivalent?

    pub fn contains(&self, x: &T) -> bool where T: PartialEq {
        match self {
            Some(y) => y == x,
            None => false,
        }
    }

    pub fn contains(&self, x: &T) -> bool where T: PartialEq {
        self.as_ref() == Some(x)
    }

@frewsxcv

@frewsxcv Not quite, due to the requested variance changes.

@soc

What does that mean @soc?

@czipperz

@czipperz The implementation is:

// Option
pub fn contains<U>(&self, x: &U) -> bool where U: PartialEq<T> {
    match self {
        Some(y) => x == y,
        None => false,
    }
}

// Result
pub fn contains<U>(&self, x: &U) -> bool where U: PartialEq<T> {
    match self {
        Ok(y) => x == y,
        Err(_) => false
    }
}

pub fn contains_err<F>(&self, f: &F) -> bool where F: PartialEq<E> {
    match self {
        Ok(_) => false,
        Err(e) => f == e
    }
}

The argument doesn't have to be of the same type as the value inside option/result, only that it knows how to compare itself to it. I. e. the operation is not invariant on the contained type, it allows an arbitrary type.

So there's no implementation of PartialEq<Option<U>> for Option<T> where U: PartialEq<T>?

There is indeed not, see #20063.

cells: add `contains` method to OptionalCell

Auto merge of rust-lang#108095 - soc:drop-contains, r=Amanieu

@Centril

@Centril methods have been removed, this issue can be closed now.

treewide: Remove option_result_contains feature

Auto merge of #108095 - soc:drop-contains, r=Amanieu

i tried to remove .contains(&y), but rewriting it to .as_ref().is_some_and(|x| x == &y) annoyed me so much i had to re/introduce Contains trait into my stdx.rs file

@univerz

@univerz As per above commit one could also replace by iter().any(...), but it is only a little bit shorter so not any less annoying. I'm sad about the outcome of this issue. :-(

@univerz

@univerz Perhaps option-ext can be of use to you!

Auto merge of #108095 - soc:drop-contains, r=Amanieu

cells: add `contains` method to OptionalCell

Merge tock#2964

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Tracking issue for `Option::contains` and `Result::contains` #62358

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Tracking issue for Option::contains and Result::contains #62358

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Mark-Simulacrum commented on Jul 4, 2019

Centril commented on Jul 4, 2019

timvermeulen commented on Jul 4, 2019

soc commented on Jul 4, 2019

Mark-Simulacrum commented on Jul 4, 2019

frewsxcv commented on Jul 6, 2019

soc commented on Jul 8, 2019

czipperz commented on Jul 14, 2019

soc commented on Jul 14, 2019

czipperz commented on Jul 14, 2019

timvermeulen commented on Jul 14, 2019

150 remaining items

soc commented on Mar 29, 2023

univerz commented on Apr 19, 2023

bjorn commented on Apr 19, 2023

soc commented on Apr 19, 2023

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Tracking issue for `Option::contains` and `Result::contains` #62358