strings

`&str` are "string slices" and (usually?) statically allocated, at least
when specified as literals.  `String`s, on the other hand, are allocated
on the heap and mutable.

rust/book/src/main.rs

@@ -92,4 +92,12 @@ fn main() {
    for x in 0..10 {
        println!("{}", x);
    }
    // strings
    let string_slice = "Hello, World!";
    let mut string = string_slice.to_string();
    println!("{} = {}", string_slice, string);
    string.push_str(" (again...)");
    println!("{}", string);
}