add iter

iter/src/main.rs

@@ -0,0 +1,54 @@
+struct Seq {
+    start: i32,
+    end: i32,
+}
+
+impl Seq {
+    pub fn new(start: i32, end: i32) -> Self {
+        Self { start, end, }
+    }
+}
+
+impl Iterator for Seq {
+    type Item = i32;
+
+    fn next(&mut self) -> Option<i32> {
+        if self.start < self.end {
+            let a = self.start;
+            self.start += 1;
+            Some(a)
+        } else {
+            None
+        }
+    }
+}
+
+fn main() {
+    test_001();
+    test_002();
+    test_003();
+}
+
+fn test_001() {
+    println!("## test001");
+    let seq = Seq::new(10, 15);
+    for a in seq {
+        println!("-> {}", a);
+    }
+}
+
+fn test_002() {
+    println!("## test002");
+    let mut seq = Seq::new(10, 15);
+    while let Some(a) = seq.next() {
+        println!("-> {}", a);
+    }
+}
+
+fn test_003() {
+    println!("## test003");
+    let mut seq = Seq::new(10, 15).take(3);
+    while let Some(a) = seq.next() {
+        println!("-> {}", a);
+    }
+}