title: A more convenient concatenation with a string literal in Rust
body: <p>In the nightly Rust it is no longer possible to designate a string literal as String <a href="https://stackoverflow.com/questions/15997206/concatenate-string-literal-with-another-string">with a "~" character</a>.</p>
  
  <p>In C++, for example, I'm using <a href="http://en.wikipedia.org/wiki/C%2B%2B11#User-defined_literals" rel="noreferrer">user-defined literals</a> to concatenate string literals without the crust of mentioning <code>std::string</code> every time:</p>
  
  <pre><code>inline std::string operator"" _s (const char* str, size_t size) {return std::string (str, size);}
  foo ("Hello, "_s + "world!");
  </code></pre>
  
  <p>Is there a similar feature existing or planned in Rust to make string literal concatenation less painful than <code>String::from_str ("Hello, ") + "world!"</code>?</p>