add en/string.md

en/src/functional-programing/iterator.md

@@ -1 +1,19 @@
 # Iterator
+
+```rust,editable
+// (all the type annotations are superfluous)
+// A reference to a string allocated in read only memory
+let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
+println!("Pangram: {}", pangram);
+
+// Iterate over words in reverse, no new string is allocated
+println!("Words in reverse");
+for word in pangram.split_whitespace().rev() {
+    println!("> {}", word);
+}
+
+// Copy chars into a vector, sort and remove duplicates
+let mut chars: Vec<char> = pangram.chars().collect();
+chars.sort();
+chars.dedup();
+```