Matching in stream-2025-04-16.md.

Author: dkorolev

stream-2025-04-16.md

@@ -62,3 +62,50 @@ fn main() {
     println!("Done!")
 }
 ```
+
+Matching: [link](https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=cd4da27c5fb79ad3405f07131d60d275).
+
+```
+#![allow(unused_variables)]
+
+fn print_string(s: &Option<String>) {
+    match s {
+        Some(s) => println!("Some string: {s}"),
+        None => println!("No string!")
+    }
+}
+
+fn main() {
+    // Basic matching.
+    let mut maybe_string = Some("foo".to_string());
+    println!("{:?}", maybe_string);
+    print_string(&maybe_string);
+    
+    maybe_string = None;
+    println!("{:?}", maybe_string);
+    print_string(&maybe_string);
+    
+    // Matching with destructuring.
+    let mut magic = (Some("foo".to_string()), Some("bar".to_string()));
+    println!("{:?}", magic);
+    
+    // Use a closure ("lambda") as an example.
+    // Note: explain need to annotate the type.
+    // Note: explain can use a simple construct of `&_`, hehe.
+    let print_magic = |arg: &(Option<String>, Option<String>)| {
+        // println!("Arg: {:?}", &arg);
+        match arg {
+            (Some(s1), Some(s2)) => println!("Both: ({s1}, {s2})."),
+            (None, Some(s2)) => println!("Second: (Zilch, {s2})."),
+            _ => println!("Something else, too lazy to type.")
+        }
+    };
+    print_magic(&magic);  // Note: try removing the `&`.
+
+    magic.0 = None;
+    print_magic(&magic);
+    
+    magic.0 = Some("hehe".to_string());
+    print_magic(&magic);
+}
+```