added strref example

Author: BartMassey

README.md

@@ -57,3 +57,4 @@ in a controlled repository now.
 * `closure-example.rs`: example of Rust closure
 * `iterator-example.rs`: example of Rust iterator
 * `lifetimes-example.rs`: example involving Rust lifetimes
+* `strref.rs`: example involving Rust string clones and copies

strref.rs

@@ -0,0 +1,35 @@
+fn main() {
+    let s = "hello".to_string();
+    let rs = &s;
+    let rrs: &&String = &rs;
+    // Prints hello.
+    println!("{}", *rrs);
+
+    let s = "hello".to_string();
+    // This takes s by reference.
+    // Clippy will warn you that you don't need to clone here.
+    let cs: String = s.clone();
+    // Prints hello.
+    println!("{}", cs);
+
+    let s = "hello".to_string();
+    let rs = &s;
+    // This takes rs by reference, but then dereferences it automatically.
+    let cs: String = rs.clone();
+    // Prints hello.
+    println!("{}", cs);
+
+    let s: &str = "hello";
+    // This would clone the &str reference, so it fails to compile.
+    // let cs: String = s.clone();
+    let cs: String = s.to_owned();
+    // Also acceptable above would have been:
+    // let cs: String = s.to_string();
+    // let cs: String = String::from(s);
+    // let cs: String = s.into();
+    // Those last two will eat a copy of s, since &str is copy, since
+    // references are copy. So you could still do this:
+    // println!("{}", s);
+    // Prints hello.
+    println!("{}", cs);
+}