1 | #ifndef LUATB_TYPED_STACK_H |
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2 | #define LUATB_TYPED_STACK_H |
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3 | |
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4 | #include <type_traits> |
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5 | #include <functional> |
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6 | #include <lua.hpp> |
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7 | #include "is_callable.h" |
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8 | #include "core/CoreIncludes.h" |
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9 | |
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10 | |
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11 | /** |
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12 | * @brief Represents a typed version of the lua stack |
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13 | * |
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14 | * We need a separate class for this because we need to specialize the functions |
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15 | * and that's not possible if we didn't specialize the class. And the logical |
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16 | * separation makes sense as well. |
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17 | */ |
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18 | class LuaTBTypedStack |
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19 | { |
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20 | public: |
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21 | |
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22 | /** |
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23 | * @brief Get a non-function argument from the lua stack and convert it to type 'T' |
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24 | * @param lua Pointer to the lua state |
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25 | * @return Top element of the lua stack with the appropriate type |
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26 | * |
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27 | * Note: Pops the value from the stack. |
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28 | */ |
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29 | template<typename T> |
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30 | static typename std::enable_if<!IsCallable<T>::value, T>::type getArgument(lua_State *lua) |
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31 | { |
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32 | T value = LuaTBTypedStack::getFromLuaStack<T>(lua); |
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33 | lua_pop(lua, 1); |
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34 | return value; |
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35 | } |
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36 | |
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37 | /** |
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38 | * @brief Get a function-type argument from the lua stack and convert it to type 'T' |
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39 | * @param lua Pointer to the lua state |
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40 | * @return Top element of the lua stack with the appropriate type |
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41 | * |
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42 | * Specialization if 'T' is a callable type (std::function). Saves the lua |
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43 | * function in the registry and constructs a function to call it again. |
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44 | * |
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45 | * Note: Pops the value from the stack. |
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46 | */ |
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47 | template<typename T> |
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48 | static typename std::enable_if<IsCallable<T>::value, T>::type getArgument(lua_State *lua) |
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49 | { |
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50 | // Here's the tricky part. Apparently, references in the registry can only |
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51 | // be called once. This is why we always have to re-add it to the registry |
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52 | // after every call. That means, we need a persistent variable for 'ref' and |
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53 | // that's only possible with a pointer in this case. |
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54 | int *ref = new int(luaL_ref(lua, LUA_REGISTRYINDEX)); |
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55 | LuaTBTypedStack::callbackRefs.push_back(std::unique_ptr<int>(ref)); |
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56 | |
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57 | // 'decltype(&T::operator())' represents the function signature of the callable object. |
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58 | return GetLuaCallback<decltype(&T::operator())>::value(lua, ref); |
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59 | } |
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60 | |
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61 | private: |
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62 | template<typename T> struct GetLuaCallback; |
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63 | |
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64 | // Gets a value from the top of the lua stack and returns it with the proper type. |
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65 | // Does not pop the value! |
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66 | /** |
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67 | * @brief Get a value from the lua stack and convert it to type 'T' |
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68 | * @param lua Pointer to the lua state |
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69 | * @return Top element of the lua stack with the appropriate type |
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70 | * |
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71 | * Note: Does NOT pop the value from the stack. |
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72 | */ |
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73 | template<typename T> static T getFromLuaStack(lua_State *lua); |
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74 | |
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75 | // This class is only valid for std::function types. The type argument will not |
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76 | // be a normal function signature because it is the signature of |
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77 | // std::function<>::operator(), which is also the reason for the 'const'. |
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78 | /** |
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79 | * @brief Needed to get a lambda to call a lua function |
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80 | * |
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81 | * We need this class, becasue we need to specify the signature of the function |
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82 | * before. |
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83 | */ |
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84 | template<typename Ret, typename... Args> |
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85 | struct GetLuaCallback<void (std::function<Ret(Args...)>::*)(Args...) const> |
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86 | { |
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87 | /** |
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88 | * @brief Get a lambda to call a lua function later |
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89 | * @param lua Pointer to the lua state |
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90 | * @param ref Pointer to the lua registry reference where the function is stored |
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91 | * @return Lambda that will call the function specified with ref |
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92 | */ |
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93 | static std::function<void (Args...)> value(lua_State *lua, int *ref) |
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94 | { |
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95 | // We can't return 'callLuaFunction' directly, because we need the |
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96 | // additional arguments 'lua' and 'ref' which we would like to hide |
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97 | // from the user. |
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98 | return [lua, ref](Args... args){callLuaFunction<Ret, Args...>(lua, ref, args...);}; |
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99 | } |
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100 | }; |
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101 | |
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102 | /** |
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103 | * @brief Pushes all arguments to the lua stack and calls a lua function afterwards |
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104 | * @param lua Pointer to the lua state |
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105 | * @param ref Pointer to the lua registry reference where the function is stored |
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106 | * @param args Arguments for the function |
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107 | */ |
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108 | template<typename Ret, typename... Args> |
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109 | static void callLuaFunction(lua_State *lua, int *ref, Args... args) |
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110 | { |
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111 | // Get the value of the callback from the registry and push it to the stack |
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112 | lua_rawgeti(lua, LUA_REGISTRYINDEX, *ref); |
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113 | |
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114 | // Duplicate it on the stack so we can save it in the registry again after |
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115 | // we called the callback. |
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116 | lua_pushvalue(lua, 1); |
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117 | |
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118 | // We pass one extra argument in case the function has no arguments at all |
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119 | pushArgumentsToLuaStack<Args...>(lua, args..., false); |
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120 | lua_pcall(lua, sizeof...(args), 0, 0); |
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121 | |
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122 | // Release the old reference and save the function in the registry again |
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123 | lua_unref(lua, *ref); |
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124 | *ref = luaL_ref(lua, LUA_REGISTRYINDEX); |
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125 | } |
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126 | |
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127 | /** |
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128 | * @brief Pushes nothing onto the stack |
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129 | * |
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130 | * This is needed in case the function has no arguments at all. Otherwise, we |
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131 | * would have a missing argument for such a function. This is also why we pass |
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132 | * a dummy argument in 'callLuaFunction', so we have at least one argument. It |
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133 | * is the termination point for the recursive template. |
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134 | */ |
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135 | template<typename T> |
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136 | static void pushArgumentsToLuaStack(lua_State *, T) |
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137 | { } |
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138 | |
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139 | /** |
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140 | * @brief Recursively pushes arguments to the lua stack |
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141 | * @param lua Pointer to the lua state |
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142 | * @param first First argument to push onto the stack |
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143 | * @param args The remaining arguments to push onto the stack |
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144 | */ |
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145 | template<typename First, typename... Args> |
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146 | static void pushArgumentsToLuaStack(lua_State *lua, First first, Args... args) |
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147 | { |
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148 | pushToLuaStack(lua, first); |
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149 | pushArgumentsToLuaStack<Args...>(lua, args...); |
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150 | } |
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151 | |
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152 | /** |
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153 | * @brief Pushes a value to the lua stack |
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154 | * @param lua Pointer to the lua state |
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155 | * @param value The value to push |
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156 | * |
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157 | * Note: Only the specializations are valid |
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158 | */ |
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159 | template<typename T> |
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160 | static void pushToLuaStack(lua_State *lua, T value); |
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161 | |
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162 | static std::list<std::unique_ptr<int> > callbackRefs; |
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163 | }; |
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164 | |
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165 | #endif // LUATB_TYPED_STACK_H |
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