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//! Collect an iterator into a slice. //! //! Rust comes with the `Iterator::collect` method for collecting an iterator's items into //! a heap-allocated `Vec` or any other type that implements `FromIterator`, but there's //! no way to collect items into a stack-allocated array without manually looping over the //! iterator. This crates provides an alternative with `collect_slice` methods that //! collect an iterator's items into a mutable slice (of a stack-allocated array or //! otherwise.) //! //! The trait is automatically implemented for any type that implements `Iterator`. //! //! # Examples //! //! ``` //! use collect_slice::CollectSlice; //! //! let mut orig = [0; 8]; //! (0..8).map(|i| i * 2).collect_slice_checked(&mut orig[..]); //! assert_eq!(orig, [0, 2, 4, 6, 8, 10, 12, 14]); //! //! let mut buf = [42; 8]; //! orig.iter() //! .map(|&x| x + 10) //! .collect_slice_checked(&mut buf[..]); //! assert_eq!(buf, [10, 12, 14, 16, 18, 20, 22, 24]); //! ``` //! //! # Usage //! //! This crate can be used through cargo by adding it as a dependency in `Cargo.toml`: //! //! ```toml //! [dependencies] //! collect_slice = "^1.2.0" //! ``` //! and importing it in the crate root: //! //! ``` //! extern crate collect_slice; //! ``` //! The provided methods can then be used by importing the trait within individual //! modules: //! //! ``` //! use collect_slice::CollectSlice; //! ``` /// An iterator that can collect into a slice. pub trait CollectSlice: Iterator { /// Loop through the iterator, sequentially writing items into the given slice until /// either the iterator runs out of items or the slice fills up. /// /// Return the number of items written. /// /// # Examples /// /// ``` /// use collect_slice::CollectSlice; /// /// let mut buf = [0; 10]; /// /// // Fill a whole slice. /// let count = (0..10).collect_slice(&mut buf[..]); /// assert_eq!(count, 10); /// assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]); /// /// // Write into a subslice /// let count = (10..20).collect_slice(&mut buf[5..7]); /// assert_eq!(count, 2); /// assert_eq!(buf, [0, 1, 2, 3, 4, 10, 11, 7, 8, 9]); /// /// // Only writes until iterator is exhausted. /// let count = (8..10).collect_slice(&mut buf[..]); /// assert_eq!(count, 2); /// assert_eq!(buf, [8, 9, 2, 3, 4, 10, 11, 7, 8, 9]); /// /// // Extra iterator items are ignored. /// let count = (20..40).collect_slice(&mut buf[..]); /// assert_eq!(count, 10); /// assert_eq!(buf, [20, 21, 22, 23, 24, 25, 26, 27, 28, 29]); /// ``` fn collect_slice(&mut self, slice: &mut [Self::Item]) -> usize; /// Perform `collect_slice()` and panic if iterator yielded too few items to fill the /// slice. /// /// If this function succeeds, the number of items written equals the size of the /// given slice. /// /// # Examples /// /// ```rust,should_panic /// use collect_slice::CollectSlice; /// /// let mut buf = [0; 10]; /// /// // Succeeds as long as entire slice is filled. /// (0..20).collect_slice_fill(&mut buf[..]); /// (0..5).collect_slice_fill(&mut buf[..5]); /// /// // Panics otherwise! /// (0..5).collect_slice_fill(&mut buf[..]); /// ``` fn collect_slice_fill(&mut self, slice: &mut [Self::Item]) { assert_eq!(self.collect_slice(slice), slice.len()); } /// Perform `collect_slice()` and panic if the slice was too small to hold all the /// items. /// /// Return the number of items written. /// /// # Examples /// /// ```rust,should_panic /// use collect_slice::CollectSlice; /// /// let mut buf = [0; 10]; /// /// // Succeeds as long as iterator yields all its items. /// let count = (0..10).collect_slice_exhaust(&mut buf[..]); /// assert_eq!(count, 10); /// let count = (0..5).collect_slice_exhaust(&mut buf[..]); /// assert_eq!(count, 5); /// /// // Panics otherwise! /// (0..20).collect_slice_exhaust(&mut buf[..]); /// /// ``` fn collect_slice_exhaust(&mut self, slice: &mut [Self::Item]) -> usize { let count = self.collect_slice(slice); assert!(self.next().is_none()); count } /// Perform `collect_slice()` and panic if there weren't enough items to fill up /// the slice or the slice was too small to hold all the items. /// /// If this function succeeds, the number of items written equals the size of the /// given slice. /// /// # Examples /// /// ``` /// use collect_slice::CollectSlice; /// /// // Succeeds as long as iteration count equals slice capacity. /// let mut buf = [0; 10]; /// (0..10).collect_slice_checked(&mut buf[..]); /// (0..5).collect_slice_checked(&mut buf[2..7]); /// ``` /// ```rust,should_panic /// use collect_slice::CollectSlice; /// /// // Panics if iterator isn't exhausted! /// let mut buf = [0; 10]; /// (0..20).collect_slice_checked(&mut buf[..]); /// ``` /// ```rust,should_panic /// use collect_slice::CollectSlice; /// /// // Panics if slice isn't filled! /// let mut buf = [0; 10]; /// (0..5).collect_slice_checked(&mut buf[..]); /// ``` fn collect_slice_checked(&mut self, slice: &mut [Self::Item]) { assert_eq!(self.collect_slice_exhaust(slice), slice.len()); } } impl<I: ?Sized> CollectSlice for I where I: Iterator { fn collect_slice(&mut self, slice: &mut [Self::Item]) -> usize { slice.iter_mut().zip(self).fold(0, |count, (dest, item)| { *dest = item; count + 1 }) } } #[cfg(test)] mod test { use super::*; #[test] fn test_basic() { let mut buf = [0; 5]; let count = (0..5).map(|i| { i + 1 }).collect_slice(&mut buf[..]); assert_eq!(count, 5); assert_eq!(buf, [1, 2, 3, 4, 5]); } #[test] fn test_under() { let mut buf = [0; 5]; let count = (0..3).map(|i| { i + 1 }).collect_slice(&mut buf[1..]); assert_eq!(count, 3); assert_eq!(buf, [0, 1, 2, 3, 0]); } #[test] fn test_over() { let mut buf = [0; 3]; let mut iter = (0..5).map(|i| { i + 1 }); let count = iter.collect_slice(&mut buf[..]); assert_eq!(count, 3); assert_eq!(buf, [1, 2, 3]); assert_eq!(iter.next().unwrap(), 4); assert_eq!(iter.next().unwrap(), 5); } #[test] fn test_checked() { let mut buf = [0; 5]; (0..5).map(|i| { i + 1 }).collect_slice_checked(&mut buf[..]); assert_eq!(buf, [1, 2, 3, 4, 5]); } #[test] #[should_panic] fn test_checked_under() { let mut buf = [0; 5]; (0..3).map(|i| { i + 1 }).collect_slice_checked(&mut buf[..]); } #[test] #[should_panic] fn test_checked_over() { let mut buf = [0; 3]; (0..5).map(|i| { i + 1 }).collect_slice_checked(&mut buf[..]); } #[test] fn test_exhaust() { let mut buf = [0; 5]; (0..3).map(|i| { i + 1 }).collect_slice_exhaust(&mut buf[..]); assert_eq!(buf, [1, 2, 3, 0, 0]); (0..5).map(|i| { i + 1 }).collect_slice_exhaust(&mut buf[..]); assert_eq!(buf, [1, 2, 3, 4, 5]); } #[test] #[should_panic] fn test_exhaust_over() { let mut buf = [0; 5]; (0..7).map(|i| { i + 1 }).collect_slice_exhaust(&mut buf[..]); } #[test] fn test_filled() { let mut buf = [0; 5]; (0..5).map(|i| { i + 1 }).collect_slice_fill(&mut buf[..]); assert_eq!(buf, [1, 2, 3, 4, 5]); (50..100).map(|i| { i + 1 }).collect_slice_fill(&mut buf[..]); assert_eq!(buf, [51, 52, 53, 54, 55]); } #[test] #[should_panic] fn test_filled_under() { let mut buf = [0; 5]; (0..3).map(|i| { i + 1 }).collect_slice_fill(&mut buf[..]); } #[test] fn test_unsized() { let mut buf = [0; 5]; let it: &mut Iterator<Item=_> = &mut (0..5).map(|i| { i + 1 }); let count = <Iterator<Item=_> as CollectSlice>::collect_slice(it, &mut buf[..]); assert_eq!(count, 5); assert_eq!(buf, [1, 2, 3, 4, 5]); } }