我搞砸了可变参数的模板,并试图锻炼一个诱人的计划。我知道它们存在,但是只是想弄乱新功能。我正在使用VS2013试用版。我创建了一个仿函数类,该仿函数类包装了从C ++端调用lua函数所需的信息。但是,我无法终生获得将模板变量压入堆栈以进行解包和工作的模板函数。我已经尝试过在网上找到的每个示例,并尝试了他们提到如何解压缩功能模板的值的所有方法。我显然缺少了一些东西。我注意到的所有示例都引用了&&引用。这是一个要求吗?
/*
These functions push an item onto the lua stack
*/
template<typename T> inline void lua_push(lua_State* L,T&& t){ static_assert(false, "Unsupported Type! Cannot set to lua stack"); }
template<> inline void lua_push<lua_CFunction>(lua_State* L,lua_CFunction&& func){ assert(L != nullptr && func != nullptr); lua_pushcfunction(L, func); }
template<> inline void lua_push<double>(lua_State* L,double&& d){ assert(L != nullptr); lua_pushnumber(L, d); }
template<> inline void lua_push<int>(lua_State* L,int&& i){ assert(L != nullptr); lua_pushinteger(L, i); }
template<> inline void lua_push<bool>(lua_State* L,bool&& b){ assert(L != nullptr); lua_pushboolean(L, b); }
template<> inline void lua_push<std::string>(lua_State* L,std::string&& s){ assert(L != nullptr); lua_pushlstring(L, s.c_str(), s.size()); }
template<> inline void lua_push<const char*>(lua_State* L,const char*&& s){ assert(L != nullptr); lua_pushstring(L, s); }
然后我想在本课中解压它
template<typename Return,typename... Args> class LuaFunctor{};
/*
A Lua function that will return a single value.
*/
template<typename Return,typename... Args> class LuaFunctor<Return(Args...)>
{
private:
//The lua state the function exists on
lua_State* m_luaState;
//Name of the function to be called in lua
std::string m_FunctionName;
public:
//Return typedef
typedef Return return_type;
//The number of arguments the functor accepts
static const int arguments = sizeof...(Args);
//Constructors
inline LuaFunctor(lua_State* L,const std::string& name) : m_luaState(L), m_FunctionName(name) {}
inline LuaFunctor(lua_State* L,const char* name) : m_luaState(L), m_FunctionName(name) {}
//Function call overload that allows the functor to act like a function call of luascript
inline Return operator()(Args&&... args)
{
//Assert that the function name does exist and luaState is pointing to something hopefully meaningful
assert(m_luaState != nullptr && m_FunctionName.size() != 0);
//Set the function
lua_getglobal(m_luaState, m_FunctionName.c_str());
//Verify Lua function is pushed onto the stack
assert(lua_isfunction(m_luaState, -1));
//If arguments exist push them onto the stack
if (sizeof...(Args) != 0)
{
/*
How do I unpack this?????
I want to unpack this into multiple functions
One for each type of argument.
*/
lua_push(m_luaState, std::forward<Args>(args))...;
}
//Call the function that is in lua
int status = lua_pcall(m_luaState, sizeof...(Args), 1, 0);
/*
If there was an error calling the function throw an exception
TODO: parse the error using luas builtin decode of the error for now just pass it on
TODO: create lua_exception
*/
if (status != 0) throw std::exception("Error calling lua function");
//Return the value request by lua, error checking is built-in to the function to verify type
return lua_get<Return>(m_luaState);
}
};
解决方法是这里。递归函数调用。尝试了我正在阅读的各种技巧,但这很简单。
/*
These functions push an item onto the lua stack
*/
template<typename First, typename... Rest> inline void lua_push(lua_State* L,First first,Rest... rest)
{
lua_push(L, first);
lua_push(L, rest...);
}
template<typename T> inline void lua_push(lua_State* L, T t){ static_assert(false, "Invalid type attemptiing to be pushed onto lua stack!"); }
template<> inline void lua_push<lua_CFunction>(lua_State* L, lua_CFunction func){ assert(L != nullptr && func != nullptr); lua_pushcfunction(L, func); }
template<> inline void lua_push<double>(lua_State* L, double d){assert(L != nullptr); lua_pushnumber(L, d); }
template<> inline void lua_push<int>(lua_State* L, int i){ assert(L != nullptr); lua_pushinteger(L, i); }
template<> inline void lua_push<bool>(lua_State* L, bool b){ assert(L != nullptr); lua_pushboolean(L, b); }
template<> inline void lua_push<std::string>(lua_State* L, std::string s){assert(L != nullptr); lua_pushlstring(L, s.c_str(), s.size()); }
template<> inline void lua_push<const char*>(lua_State* L,const char* s){ assert(L != nullptr); lua_pushstring(L, s); }
该代码现在可以完美运行。
template<typename Return,typename... Args> class LuaFunctor<Return(Args...)>
{
private:
//The lua state the function exists on
lua_State* m_luaState;
//Name of the function to be called in lua
std::string m_FunctionName;
public:
//Return typedef
typedef Return return_type;
//The number of arguments the functor accepts
static const int arguments = sizeof...(Args);
//Constructors
inline LuaFunctor(lua_State* L,const std::string& name) : m_luaState(L), m_FunctionName(name) {}
inline LuaFunctor(lua_State* L,const char* name) : m_luaState(L), m_FunctionName(name) {}
//Function call overload that allows the functor to act like a function call of luascript
inline Return operator()(Args... args)
{
//Assert that the function name does exist and luaState is pointing to something hopefully meaningful
assert(m_luaState != nullptr && m_FunctionName.size() != 0);
//Set the function
lua_getglobal(m_luaState, m_FunctionName.c_str());
//Verify Lua function is pushed onto the stack
assert(lua_isfunction(m_luaState, -1));
//If arguments exist push them onto the stack
if (sizeof...(Args) != 0) lua_push(m_luaState, args...);
//Call the function that is in lua
int status = lua_pcall(m_luaState, sizeof...(Args), 1, 0);
/*
If there was an error calling the function throw an exception
TODO: parse the error using luas builtin decode of the error for now just pass it on
TODO: create lua_exception
*/
if (status != 0)
{
report_errors(status);
throw std::exception("Error calling lua function");
}
//Return the value request by lua, error checking is built-in to the function to verify type
return lua_get<Return>(m_luaState);
}
};
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我来说两句