murarth / assert_matches Goto Github PK

Consider this example(I would do a playground one if assert_matches were accesible there):

#[derive(Debug)]
pub enum Error {
    Lowercase { name: String },
}

fn do_something(n: String) -> Result<(), Error> {
    match n {
        name if name.chars().any(|c| !c.is_lowercase()) => Err(Error::Lowercase { name }),
        _ => panic!("All good"),
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use assert_matches::assert_matches;

    #[test]
    fn example() {
        let name = "BazinGa";
        let e: Result<(), Error> = Err(Error::Lowercase {
            name: "".to_owned(),
        });
        assert_matches!(do_something(name.to_owned()), e);
    }
}

Here are a few issues:

• if you place error in assert_matches directly it will not compile.
• if you make it a separate e variable the compiler will complain that it is not used both in place of declaration and usage
• finally while the in the passing test the error type parsed correctly(if you will add another one and change the variant it should fail) but the name field name is not mathed correctly.

Your assert_matches macro is more expressive than that in the matches crate.

My project should probably just switch to this crate, though. We do not use matches macro anywhere.

Hi!

I found myself implementing a very similar macro a few times. I called it assert_pat, but it did virtually the same thing. Today I thought I should create an RFC proposing that my macro is added to the standard library. I find it very useful and ergonomic whenever you need to assert equality on something that does not implement Eq, but that can be matched by a destructure. For example, when using error-chain this is very needed, since the errors generated by that library does not implement Eq.

However. In my research I found this crate, which is awesome! But have you thought about suggesting it be included in the standard library?