Add lifetimes example

lifetimes/src/main.rs

@@ -0,0 +1,47 @@
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+    if x.len() > y.len() {
+        x
+    } else {
+        y
+    }
+}
+
+// No need to specify lifetime of second param since it is not used in the function
+fn longest_always_first_param<'a>(x: &'a str, _y: &str) -> &'a str {
+    x
+}
+
+#[derive(Debug)]
+struct Excerpt<'a> {
+    part: &'a str,
+}
+
+impl<'a> Excerpt<'a> {
+    // Because of the lifetime elision rules, no need to add lifetimes here, compiler is smart enough to figure it out
+    fn announce_and_return_part(&self, announcement: &str) -> &str {
+        println!("Attention please: {}", announcement);
+        self.part
+    }
+}
+
+fn main() {
+    let string1 = String::from("abcd");
+    let string2 = "xyz";
+    let _s: &'static str = "I have a static lifetime and will live until the program ends.";
+
+    let result = longest(string1.as_str(), string2);
+    println!("The longest string is {}", result);
+    println!(
+        "The longest string is maybe {}?",
+        longest_always_first_param(string1.as_str(), string2)
+    );
+
+    let novel = String::from("Call me Ishmael. Some years ago ...");
+    let first_sentence = novel.split('.').next().expect("Could not find a '.'");
+    let i = Excerpt {
+        part: first_sentence,
+    };
+
+    println!("excerpt: {:?}", i);
+    i.announce_and_return_part("hello");
+}