From 66e7b9956833678a7911abc362031774f31ed211 Mon Sep 17 00:00:00 2001
From: Jordan Gong <jordan.gong@protonmail.com>
Date: Tue, 8 Sep 2020 20:18:34 +0800
Subject: Iterate with closures

---
 iterators/src/lib.rs | 125 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 iterators/src/lib.rs

(limited to 'iterators/src/lib.rs')

diff --git a/iterators/src/lib.rs b/iterators/src/lib.rs
new file mode 100644
index 0000000..01ffec3
--- /dev/null
+++ b/iterators/src/lib.rs
@@ -0,0 +1,125 @@
+#[derive(PartialEq, Debug)]
+struct Shoe {
+    size: u32,
+    style: String,
+}
+
+fn shoes_in_my_size(shoes: Vec<Shoe>, shoe_size: u32) -> Vec<Shoe> {
+    shoes.into_iter().filter(|s| s.size == shoe_size).collect()
+}
+
+struct Counter {
+    count: u32,
+}
+
+impl Counter {
+    fn new() -> Counter {
+        Counter { count: 0 }
+    }
+}
+
+impl Iterator for Counter {
+    type Item = u32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.count < 5 {
+            self.count += 1;
+            Some(self.count)
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn interator_demostration() {
+        let v1 = vec![1, 2, 3];
+
+        let mut v1_iter = v1.iter();
+
+        assert_eq!(v1_iter.next(), Some(&1));
+        assert_eq!(v1_iter.next(), Some(&2));
+        assert_eq!(v1_iter.next(), Some(&3));
+        assert_eq!(v1_iter.next(), None);
+    }
+
+    #[test]
+    fn iterator_sum() {
+        let v1 = vec![1, 2, 3];
+
+        let v1_iter = v1.iter();
+
+        let total: i32 = v1_iter.sum();
+
+        assert_eq!(total, 6);
+    }
+
+    #[test]
+    fn iterator_adaptor() {
+        let v1: Vec<i32> = vec![1, 2, 3];
+
+        let v2: Vec<_> = v1.iter().map(|x| x + 1).collect();
+
+        assert_eq!(v2, vec![2, 3, 4]);
+    }
+
+    use super::*;
+    #[test]
+    fn filter_by_size() {
+        let shoes = vec![
+            Shoe {
+                size: 10,
+                style: String::from("sneaker"),
+            },
+            Shoe {
+                size: 13,
+                style: String::from("sandal"),
+            },
+            Shoe {
+                size: 10,
+                style: String::from("boot"),
+            },
+        ];
+
+        let in_my_size = shoes_in_my_size(shoes, 10);
+
+        assert_eq!(
+            in_my_size,
+            vec![
+                Shoe {
+                    size: 10,
+                    style: String::from("sneaker"),
+                },
+                Shoe {
+                    size: 10,
+                    style: String::from("boot"),
+                },
+            ]
+        );
+    }
+
+    #[test]
+    fn calling_next_directly() {
+        let mut counter = Counter::new();
+
+        assert_eq!(counter.next(), Some(1));
+        assert_eq!(counter.next(), Some(2));
+        assert_eq!(counter.next(), Some(3));
+        assert_eq!(counter.next(), Some(4));
+        assert_eq!(counter.next(), Some(5));
+        assert_eq!(counter.next(), None);
+    }
+
+    #[test]
+    fn using_other_iterator_trait_methods() {
+        let sum: u32 = Counter::new()
+            .zip(Counter::new().skip(1))
+            .map(|(a, b)| a * b)
+            .filter(|x| x % 3 == 0)
+            .sum();
+
+        assert_eq!(sum, 18);
+    }
+}
-- 
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