add boxing; episode 14

Author: Byron

Cargo.lock

@@ -1,2 +1,2 @@
 [workspace]
-members = ["./ownership-and-borrowing", "options-and-results", "errors", "iterators", "strings"]
+members = ["./ownership-and-borrowing", "options-and-results", "errors", "iterators", "strings", "boxing"]

Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "boxing"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

boxing/Cargo.toml

@@ -0,0 +1,50 @@
+fn make_iterator(select: bool) -> Box<dyn Iterator<Item = u32>> {
+    if select {
+        Box::new([1u32].into_iter())
+    } else {
+        Box::new(vec![0u32].into_iter())
+    }
+}
+
+fn use_iterator(iter: impl Iterator<Item = u32>) {
+    for num in iter {
+        println!("{}", num)
+    }
+}
+
+fn use_dyn_iterator(iter: &mut dyn Iterator<Item = u32>) {
+    for num in iter {
+        println!("{}", num)
+    }
+}
+
+struct MyVec<'a> {
+    inner: Vec<&'a String>,
+}
+
+impl<'a> MyVec<'a> {
+    fn iter(&self) -> Box<dyn Iterator<Item = &String> + '_> {
+        Box::new(self.inner.iter().copied())
+    }
+}
+
+fn main() {
+    use_iterator(make_iterator(true));
+    use_iterator([1u32].into_iter());
+
+    use_dyn_iterator(&mut [1u32].into_iter());
+    use_dyn_iterator(&mut make_iterator(true));
+
+    let other = vec![2u32];
+    let empty: Vec<u32>;
+    let iter = if false {
+        empty = Vec::new();
+        empty.iter()
+    } else {
+        other.iter()
+    };
+
+    for item in iter {
+        println!("{}", item)
+    }
+}