LeechCraft  0.6.70-13729-g7046a9d2a7
Modular cross-platform feature rich live environment.
visitor.h
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29 
30 #pragma once
31 
32 #include <variant>
33 #include "void.h"
34 #include "util.h"
35 
36 namespace LC
37 {
38 namespace Util
39 {
40  namespace detail
41  {
42  template<typename... Bases>
43  struct VisitorBase : std::decay_t<Bases>...
44  {
45  VisitorBase (Bases&&... bases)
46  : std::decay_t<Bases> { std::forward<Bases> (bases) }...
47  {
48  }
49 
50  using std::decay_t<Bases>::operator()...;
51  };
52 
53  template<class... Ts> struct Overloaded : Ts...
54  {
55  using Ts::operator()...;
56  };
57  template<class... Ts> Overloaded (Ts...) -> Overloaded<Ts...>;
58  }
59 
60  template<typename... Vars, typename... Args>
61  decltype (auto) Visit (const std::variant<Vars...>& v, Args&&... args)
62  {
63  return std::visit (detail::Overloaded { std::forward<Args> (args)... }, v);
64  }
65 
66  template<typename... Vars, typename... Args>
67  decltype (auto) Visit (std::variant<Vars...>& v, Args&&... args)
68  {
69  return std::visit (detail::Overloaded { std::forward<Args> (args)... }, v);
70  }
71 
72  namespace detail
73  {
74  struct VisitorFinallyTag {};
75  }
76 
77  template<typename FinallyFunc, typename... Args>
78  class Visitor
79  {
80  detail::VisitorBase<Args...> Base_;
81 
82  FinallyFunc Finally_;
83  public:
84  Visitor (Args&&... args)
85  : Base_ { std::forward<Args> (args)... }
86  {
87  }
88 
89  Visitor (const detail::VisitorFinallyTag&, Args&&... args, FinallyFunc&& func)
90  : Base_ { std::forward<Args> (args)... }
91  , Finally_ { std::forward<FinallyFunc> (func) }
92  {
93  }
94 
95  template<typename T>
96  decltype (auto) operator() (const T& var) const
97  {
98  if constexpr (std::is_same_v<FinallyFunc, Void>)
99  return Visit (var, Base_);
100  else
101  {
102  const auto guard = MakeScopeGuard (Finally_);
103  return Visit (var, Base_);
104  }
105  }
106 
107  template<typename F>
108  Visitor<F, detail::VisitorBase<Args...>> Finally (F&& func)
109  {
110  return { detail::VisitorFinallyTag {}, std::move (Base_), std::forward<F> (func) };
111  }
112  };
113 
114  template<typename... Args>
115  Visitor (Args&&...) -> Visitor<Void, Args...>;
116 
117  template<typename T, typename... Args>
118  auto InvokeOn (T&& t, Args&&... args)
119  {
120  return detail::VisitorBase<Args...> { std::forward<Args> (args)... } (std::forward<T> (t));
121  }
122 }
123 }
Visitor< F, detail::VisitorBase< Args... > > Finally(F &&func)
Definition: visitor.h:108
Visitor(const detail::VisitorFinallyTag &, Args &&... args, FinallyFunc &&func)
Definition: visitor.h:89
Overloaded(Ts...) -> Overloaded< Ts... >
STL namespace.
Visitor(Args &&... args)
Definition: visitor.h:84
auto Visit(const Either< Left, Right > &either, Args &&... args)
Definition: either.h:224
auto InvokeOn(T &&t, Args &&... args)
Definition: visitor.h:118
VisitorBase(Bases &&... bases)
Definition: visitor.h:45
detail::ScopeGuard< F > MakeScopeGuard(const F &f)
Returns an object performing passed function on scope exit.
Definition: util.h:157
Visitor(Args &&...) -> Visitor< Void, Args... >
Definition: constants.h:35