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//! This crate provides a way to create iterators on the fly. //! //! It currently only consists of the `iter_vals` macro to archive that. /// Creates an iterator for all the given values. /// /// # Examples /// /// You can use it to return an iterator over literals: /// /// ``` /// use iter_vals::iter_vals; /// /// #[derive(Debug, PartialEq)] /// enum Media { /// Book, /// Newspaper, /// TV, /// PC, /// } /// /// use Media::*; /// /// impl Media { /// fn digital() -> impl Iterator<Item = Media> { /// iter_vals!(TV, PC) /// } /// /// fn non_digital() -> impl Iterator<Item = Media> { /// iter_vals!(Book, Newspaper) /// } /// } /// /// let mut digital = Media::digital(); /// assert_eq!(digital.next(), Some(TV)); /// assert_eq!(digital.next(), Some(PC)); /// assert_eq!(digital.next(), None); /// /// let mut non_digital = Media::non_digital(); /// assert_eq!(non_digital.next(), Some(Book)); /// assert_eq!(non_digital.next(), Some(Newspaper)); /// assert_eq!(non_digital.next(), None); /// ``` /// /// You can conditionally include values. /// This can be useful to return a variable number of values without having to allocate: /// /// ``` /// use iter_vals::iter_vals; /// /// fn next_numbers(start: i32, include_first_number: bool) -> impl Iterator<Item = i32> { /// iter_vals!( /// [..= include_first_number; start + 1], /// (start + 2), /// (start + 3) /// ) /// } /// /// let mut next_nums = next_numbers(5, true); /// assert_eq!(next_nums.next(), Some(6)); /// assert_eq!(next_nums.next(), Some(7)); /// assert_eq!(next_nums.next(), Some(8)); /// assert_eq!(next_nums.next(), None); /// /// let mut next_nums = next_numbers(5, false); /// assert_eq!(next_nums.next(), Some(7)); /// assert_eq!(next_nums.next(), Some(8)); /// assert_eq!(next_nums.next(), None); /// ``` /// /// You can expand other iterators inside the iterator you return. /// This can be especially useful, when dealing with `Option`s: /// /// ``` /// use iter_vals::iter_vals; /// /// fn make_iter(num1: i32, num2: Option<i32>, num3: i32) -> impl Iterator<Item = i32> { /// iter_vals!( /// num1, /// [.. num2], /// num3 /// ) /// } /// /// let mut nums = make_iter(1, Some(2), 3); /// assert_eq!(nums.next(), Some(1)); /// assert_eq!(nums.next(), Some(2)); /// assert_eq!(nums.next(), Some(3)); /// assert_eq!(nums.next(), None); /// /// let mut nums = make_iter(1, None, 3); /// assert_eq!(nums.next(), Some(1)); /// assert_eq!(nums.next(), Some(3)); /// assert_eq!(nums.next(), None); /// /// let mut nums = iter_vals!(1, [.. vec![2, 2]], 3); /// assert_eq!(nums.next(), Some(1)); /// assert_eq!(nums.next(), Some(2)); /// assert_eq!(nums.next(), Some(2)); /// assert_eq!(nums.next(), Some(3)); /// assert_eq!(nums.next(), None); /// ``` /// /// # Note /// /// If you want to return computed values, you currently have to put them in parenthesis for that /// to work, because of a limitation in the macro system. /// /// This will **not** work: /// /// ```no_compile /// use iter_vals::iter_vals; /// /// let nums: Vec<_> = iter_vals!(1 + 1, 2 + 2, 3 + 3).collect(); /// assert_eq!(nums, vec![2, 4, 6]); /// ``` /// /// But this will: /// /// ``` /// use iter_vals::iter_vals; /// /// let nums: Vec<_> = iter_vals!((1 + 1), (2 + 2), (3 + 3)).collect(); /// assert_eq!(nums, vec![2, 4, 6]); /// ``` #[macro_export] macro_rules! iter_vals { () => { core::iter::empty() }; ([..= $cond:expr ; $val:expr]) => { if $cond { Some($val) } else { None }.into_iter() }; ([.. $val:expr]) => { $val.into_iter() }; ($val:expr) => { core::iter::once($val) }; ($first_val:tt, $($other_vals:tt),*) => { iter_vals!($first_val) $( .chain(iter_vals!($other_vals)) )* }; } #[cfg(test)] mod tests { #[test] fn basic_vals() { assert_eq!(iter_vals!(1, 2, 3).collect::<Vec<_>>(), vec![1, 2, 3]); assert_eq!(iter_vals!("this", "is", "a", "test").collect::<Vec<_>>(), vec!["this", "is", "a", "test"]); } #[test] fn empty() { assert_eq!(iter_vals!().collect::<Vec<i32>>(), vec![]); } #[test] fn conditional() { assert_eq!(iter_vals!([..= 1 == 1; 5], [..= 1 == 2; 10]).collect::<Vec<_>>(), vec![5]); } #[test] fn expansion() { assert_eq!(iter_vals!([.. vec![1, 2, 3]], [.. Some(4)]).collect::<Vec<_>>(), vec![1, 2, 3, 4]); } #[test] fn mixed() { assert_eq!(iter_vals!( 1, [..= 2 % 2 == 1; 2], 3, [..= 4 % 2 == 0; 4], [.. vec![5, 6, 7]] ).collect::<Vec<_>>(), vec![1, 3, 4, 5, 6, 7] ); } }