From 4dfc11d74ab02ac5765ae5d08fb750c91f4744b4 Mon Sep 17 00:00:00 2001
From: Hunter Kvalevog <hunter@kvog.sh>
Date: Fri, 2 Oct 2026 21:53:51 -0500
Subject: rustlings: move to rust/

---
 rust/rustlings/exercises/16_lifetimes/README.md    | 22 +++++++++++++++++
 .../rustlings/exercises/16_lifetimes/lifetimes1.rs | 28 ++++++++++++++++++++++
 .../rustlings/exercises/16_lifetimes/lifetimes2.rs | 20 ++++++++++++++++
 .../rustlings/exercises/16_lifetimes/lifetimes3.rs | 16 +++++++++++++
 4 files changed, 86 insertions(+)
 create mode 100644 rust/rustlings/exercises/16_lifetimes/README.md
 create mode 100644 rust/rustlings/exercises/16_lifetimes/lifetimes1.rs
 create mode 100644 rust/rustlings/exercises/16_lifetimes/lifetimes2.rs
 create mode 100644 rust/rustlings/exercises/16_lifetimes/lifetimes3.rs

(limited to 'rust/rustlings/exercises/16_lifetimes')

diff --git a/rust/rustlings/exercises/16_lifetimes/README.md b/rust/rustlings/exercises/16_lifetimes/README.md
new file mode 100644
index 0000000..91373f7
--- /dev/null
+++ b/rust/rustlings/exercises/16_lifetimes/README.md
@@ -0,0 +1,22 @@
+# Lifetimes
+
+Lifetimes tell the compiler how to check whether references live long
+enough to be valid in any given situation. For example lifetimes say
+"make sure parameter 'a' lives as long as parameter 'b' so that the return
+value is valid".
+
+They are only necessary on borrows, i.e. references,
+since copied parameters or moves are owned in their scope and cannot
+be referenced outside. Lifetimes mean that calling code of e.g. functions
+can be checked to make sure their arguments are valid. Lifetimes are
+restrictive of their callers.
+
+If you'd like to learn more about lifetime annotations, the
+[lifetimekata](https://tfpk.github.io/lifetimekata/) project
+has a similar style of exercises to Rustlings, but is all about
+learning to write lifetime annotations.
+
+## Further information
+
+- [Lifetimes (in Rust By Example)](https://doc.rust-lang.org/stable/rust-by-example/scope/lifetime.html)
+- [Validating References with Lifetimes](https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html)
diff --git a/rust/rustlings/exercises/16_lifetimes/lifetimes1.rs b/rust/rustlings/exercises/16_lifetimes/lifetimes1.rs
new file mode 100644
index 0000000..683bd75
--- /dev/null
+++ b/rust/rustlings/exercises/16_lifetimes/lifetimes1.rs
@@ -0,0 +1,28 @@
+// The Rust compiler needs to know how to check whether supplied references are
+// valid, so that it can let the programmer know if a reference is at risk of
+// going out of scope before it is used. Remember, references are borrows and do
+// not own their own data. What if their owner goes out of scope?
+
+// TODO: Fix the compiler error by updating the function signature.
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+    if x.len() > y.len() {
+        x
+    } else {
+        y
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_longest() {
+        assert_eq!(longest("abcd", "123"), "abcd");
+        assert_eq!(longest("abc", "1234"), "1234");
+    }
+}
diff --git a/rust/rustlings/exercises/16_lifetimes/lifetimes2.rs b/rust/rustlings/exercises/16_lifetimes/lifetimes2.rs
new file mode 100644
index 0000000..ebbc99c
--- /dev/null
+++ b/rust/rustlings/exercises/16_lifetimes/lifetimes2.rs
@@ -0,0 +1,20 @@
+// Don't change this function.
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+    if x.len() > y.len() {
+        x
+    } else {
+        y
+    }
+}
+
+fn main() {
+    // TODO: Fix the compiler error by moving one line.
+
+    let string1 = String::from("long string is long");
+    let string2 = String::from("xyz");
+    let result;
+    {
+        result = longest(&string1, &string2);
+    }
+    println!("The longest string is '{result}'");
+}
diff --git a/rust/rustlings/exercises/16_lifetimes/lifetimes3.rs b/rust/rustlings/exercises/16_lifetimes/lifetimes3.rs
new file mode 100644
index 0000000..91e3922
--- /dev/null
+++ b/rust/rustlings/exercises/16_lifetimes/lifetimes3.rs
@@ -0,0 +1,16 @@
+// Lifetimes are also needed when structs hold references.
+
+// TODO: Fix the compiler errors about the struct.
+struct Book<'a> {
+    author: &'a str,
+    title: &'a str,
+}
+
+fn main() {
+    let book = Book {
+        author: "George Orwell",
+        title: "1984",
+    };
+
+    println!("{} by {}", book.title, book.author);
+}
-- 
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