hphp/util/match.h

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-2014 Facebook, Inc. (http://www.facebook.com)     |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16 #ifndef incl_HPHP_UTIL_MATCH_H_
  17 #define incl_HPHP_UTIL_MATCH_H_
  18
  19 #include <utility>
  20
  21 #include <boost/variant.hpp>
  22
  23 namespace HPHP {
  24
  25 //////////////////////////////////////////////////////////////////////
  26
  27 /*
  28  * This is a utility for short-hand visitors (using lambdas) with
  29  * boost::apply_visitor.
  30  *
  31  * Usage e.g.:
  32  *
  33  *   match<return_type>(
  34  *     thing,
  35  *     [&] (TypeA a) { ... },
  36  *     [&] (TypeB b) { ... }
  37  *   );
  38  */
  39
  40 //////////////////////////////////////////////////////////////////////
  41
  42 namespace match_detail {
  43
  44 template<class Ret, class... Lambdas> struct visitor;
  45
  46 template<class Ret, class L, class... Lambdas>
  47 struct visitor<Ret,L,Lambdas...> : L, visitor<Ret,Lambdas...> {
  48   using L::operator();
  49   using visitor<Ret,Lambdas...>::operator();
  50   visitor(L l, Lambdas&&... lambdas)
  51     : L(l)
  52     , visitor<Ret,Lambdas...>(std::forward<Lambdas>(lambdas)...)
  53   {}
  54 };
  55
  56 template<class Ret, class L>
  57 struct visitor<Ret,L> : L {
  58   typedef Ret result_type;
  59   using L::operator();
  60   /* implicit */ visitor(L l) : L(l) {}
  61 };
  62
  63 template<class Ret> struct visitor<Ret> {
  64   typedef Ret result_type;
  65   visitor() {}
  66 };
  67
  68 template<class Ret, class... Funcs>
  69 visitor<Ret,Funcs...> make_visitor(Funcs&&... funcs) {
  70   return { std::forward<Funcs>(funcs)... };
  71 }
  72
  73 }
  74
  75 template<class Ret, class Var, class... Funcs>
  76 Ret match(Var&& v, Funcs&&... funcs) {
  77   return boost::apply_visitor(
  78     match_detail::make_visitor<Ret>(std::forward<Funcs>(funcs)...),
  79     std::forward<Var>(v)
  80   );
  81 }
  82
  83 //////////////////////////////////////////////////////////////////////
  84
  85 }
  86
  87 #endif