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//! Extension traits for `std::Result`. /// Extension trait with useful methods for [`std::result::Result`]. /// /// [`std::result::Result`]: https://doc.rust-lang.org/std/result/enum.Result.html pub trait ResultExt<T, E> { /// Combines `self` and another `Result`. /// /// If `self` is `Ok(s)` and `other` is `Ok(o)`, this method returns `Ok((s, o))`. /// Otherwise, if the `self` is `Ok(s)` and `other` is `Err(e)`, this method returns `Err(e)`. /// Otherwise, `self` is `Err(e)` and this method returns `Err(e)` (`other` is not taken into /// account, as in short circuit calculations). /// /// # Examples /// /// ``` /// use stdext::prelude::*; /// /// let x = Ok(1); /// let y = Ok("hi"); /// let z: Result<i32, &str> = Err("error"); /// let z2: Result<i32, &str> = Err("other_error"); /// /// assert_eq!(x.combine(y), Ok((1, "hi"))); /// assert_eq!(x.combine(z), Err("error")); /// assert_eq!(z.combine(z2), Err("error")); /// ``` fn combine<U>(self, other: Result<U, E>) -> Result<(T, U), E>; /// Combines `self` and another `Result` with function `f`. /// /// If `self` is `Ok(s)` and `other` is `Ok(o)`, this method returns `Ok(f(s, o))`. /// Otherwise, if the `self` is `Ok(s)` and `other` is `Err(e)`, this method returns `Err(e)`. /// Otherwise, `self` is `Err(e)` and this method returns `Err(e)` (`other` is not taken into /// account, as in short circuit calculations). /// /// # Examples /// /// ``` /// use stdext::prelude::*; /// /// let x = Ok(1); /// let y = Ok(2); /// let z: Result<i32, &str> = Err("error"); /// let z2: Result<i32, &str> = Err("other_error"); /// /// assert_eq!(x.combine_with(y, |l, r| l + r), Ok(3)); /// assert_eq!(x.combine_with(z, |l, r| l + r), Err("error")); /// assert_eq!(z.combine_with(z2, |l, r| l + r), Err("error")); /// ``` /// /// [`zip_with`]: https://doc.rust-lang.org/std/Result/enum.Result.html#method.zip_with fn combine_with<U, F, R>(self, other: Result<U, E>, f: F) -> Result<R, E> where F: FnOnce(T, U) -> R; } impl<T, E> ResultExt<T, E> for Result<T, E> { fn combine<U>(self, other: Result<U, E>) -> Result<(T, U), E> { match (self, other) { (Ok(left), Ok(right)) => Ok((left, right)), (Ok(_), Err(err)) => Err(err), (Err(err), _) => Err(err), } } fn combine_with<U, F, R>(self, other: Result<U, E>, f: F) -> Result<R, E> where F: FnOnce(T, U) -> R, { self.combine(other).map(|(l, r)| f(l, r)) } } #[cfg(test)] mod tests { use super::*; #[test] fn combine() { // Test vector of (left, right, expected) values. let test_vector = vec![ (Ok(1), Ok(2), Ok((1, 2))), (Ok(1), Err("right"), Err("right")), (Err("left"), Ok(2), Err("left")), (Err("left"), Err("right"), Err("left")), ]; for (left, right, expected) in test_vector { assert_eq!(left.combine(right), expected); } } #[test] fn combine_with() { fn f(l: i32, r: i32) -> i32 { l + r }; // Test vector of (left, right, expected) values. let test_vector = vec![ (Ok(1), Ok(2), Ok(3)), (Ok(1), Err("right"), Err("right")), (Err("left"), Ok(2), Err("left")), (Err("left"), Err("right"), Err("left")), ]; for (left, right, expected) in test_vector { assert_eq!(left.combine_with(right, f), expected); } } }