lib: implement column iterator

Signed-off-by: Matej Focko <me@mfocko.xyz>

src/iterators/column_iterator.rs

@@ -0,0 +1,25 @@
+pub struct ColumnIterator<'a, T> {
+    map: &'a [Vec<T>],
+    column: usize,
+
+    i: usize,
+}
+
+impl<'a, T> ColumnIterator<'a, T> {
+    pub fn new(map: &'a [Vec<T>], column: usize) -> ColumnIterator<'a, T> {
+        Self { map, column, i: 0 }
+    }
+}
+
+impl<'a, T> Iterator for ColumnIterator<'a, T> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.i >= self.map.len() {
+            return None;
+        }
+
+        self.i += 1;
+        Some(&self.map[self.i - 1][self.column])
+    }
+}

src/iterators/mod.rs

@@ -0,0 +1,2 @@
+mod column_iterator;
+pub use column_iterator::*;

src/lib.rs

@@ -10,5 +10,8 @@ pub use testing::*;
 mod vectors;
 pub use vectors::*;
 
+mod iterators;
+pub use iterators::*;
+
 mod data_structures;
 pub use data_structures::*;