lass='rusttest'>fn main() {
    let mut s = &quot;Hello&quot;.to_string(); // mut s: String
println!(&quot;{}&quot;, s);

s.push_str(&quot;, world.&quot;);
println!(&quot;{}&quot;, s);
}</span><pre class='rust rust-example-rendered'>
<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>s</span> <span class='op'>=</span> <span class='string'>&quot;Hello&quot;</span>.<span class='ident'>to_string</span>(); <span class='comment'>// mut s: String</span>
<span class='macro'>println</span