Kaguya

C++ binding to Lua

Licensed under Boost Software License

Requirements

• Lua 5.1 to 5.3 (recommended: 5.3)
• C++03 compiler with boost library or C++11 compiler(gcc 4.8+,clang 3.4+,MSVC2015) without boost.

Tested Environment

Introduction

Kaguya is a Lua binding library for C++

• header-file only
• seamless access to lua elements

Usage

add "kaguya/include" directory to "header search path" of your project.

Or generate single header file and add it to your project.

cd  utils
python generate_one_header.py > ../kaguya.hpp

Create Lua context

#include "kaguya/kaguya.hpp"
int main()
{
  kaguya::State state;
  state.dofile("/path/to/script.lua");
}

Or use an existing lua state

extern "C" int luaopen_modulename(lua_State *L)
{
	kaguya::State state(l);
	kaguya::LuaTable module = state.newTable();
	module["function"] = kaguya::function(somefunction);
	return module.push();//number of return lib
}

Running Lua code

kaguya::State state;
state("a = 'test'");//load and execute from string
state.dofile("path/to/luascript.lua");//load and execute from file

kaguya::LuaFunction f1 = state.loadfile("path/to/luascript.lua");//load file without executing it
f1();//execute
kaguya::LuaFunction f2 = state.loadstring("a = 'test'");//load string without executing it
f2();//execute

Accessing values

kaguya::State state;
state("a = \"test\"");
std::string a_value = state["a"];
assert(a_value == "test");

state["tbl"] = kaguya::NewTable();//tbl ={};
state["tbl"]["value"] = 1;//tbl.value = 1 in lua

state["tbl"] = kaguya::TableData{ 23,"test",{"key","value"}}; //using initializer list(C++11)
state("assert(tbl[1] == 23)");
state("assert(tbl[2] == 'test')");
state("assert(tbl['key'] == 'value')");

Retain Lua value from C++

LuaRef type is like a Variant type. You can use it for holding a Lua-value in native code.

kaguya::State state;
state["a"] = "test";
kaguya::LuaRef a = state["a"];
assert(a == "test");

state["tbl"] = kaguya::NewTable();//tbl ={};
kaguya::LuaTable tbl = state["tbl"];//holding Lua Table
tbl["value"] = 1;//tbl.value = 1 in lua
state("assert(tbl.value == 1)");

Call lua function

int ret = state["math"]["abs"](-32);//call math.abs of Lua function
assert(ret == 32);
//or
auto ret = state["math"]["abs"].call<int>(-32);//call math.abs of Lua function
assert(ret == 32);

Multiple Results from Lua

state("multresfun =function() return 1,2,4 end");//registering multiple results function
int a, b, c;
kaguya::tie(a, b, c) = state["multresfun"]();
assert(a == 1 && b == 2 && c == 4 );
//or
std::tuple<int,int,int> result_tuple = state["multresfun"].call<std::tuple<int,int,int>>();
TEST_EQUAL(std::get<0>(result_tuple), 1);
TEST_EQUAL(std::get<1>(result_tuple), 2);
TEST_EQUAL(std::get<2>(result_tuple), 4);

Registering Classes

struct ABC
{
	ABC():v_(0) {}
	ABC(int value) :v_(value) {}
	int value()const { return v_; }
	void setValue(int v) { v_ = v; }
	void overload1() {std::cout << "call overload1"<<std::endl; }
	void overload2(int) {std::cout << "call overload2"<<std::endl; }
private:
	int v_;
};
state["ABC"].setClass(kaguya::UserdataMetatable<ABC>()
	.setConstructors<ABC(),ABC(int)>()
	.addFunction("get_value", &ABC::value)
	.addFunction("set_value", &ABC::setValue)
	.addOverloadedFunctions("overload", &ABC::overload1, &ABC::overload2)
	.addStaticFunction("nonmemberfun", [](ABC* self,int){return 1;})//c++11 lambda function
	);

--Lua
abc = ABC.new()--call default constructor
assert(0 == abc:get_value())
abc = ABC.new(42)--call (int) constructor
assert(42 == abc:get_value())
abc:set_value(30)
assert(30 == abc:get_value())
abc:overload() -- call overload1
abc:overload(1) --call overload2

Registering inheritance

struct Base
{
	int a;
};
struct Base2
{
	int a2;
};
struct Derived:Base
{
	int b;
};
struct MultipleInheritance:Base,Base2
{
	int b;
};
int base_function(Base* b) {
	b->a = 1;
	return b->a;
}
//
kaguya::State state;
state["Base"].setClass(kaguya::UserdataMetatable<Base>()
	.addFunction("a", &Base::a)
	);
state["Derived"].setClass(kaguya::UserdataMetatable<Derived, Base>()
	.addFunction("b", &Derived::b)
	);

//can use kaguya::MultipleBase<BaseTypes...> for multiple inheritance class
state["MultipleInheritance"].setClass(kaguya::UserdataMetatable<MultipleInheritance, kaguya::MultipleBase<Base, Base2> >()
	.addFunction("b", &MultipleInheritance::b)
	);

state["base_function"] = &base_function;
Derived derived;
state["base_function"](&derived);//Base arguments function
state("assert(1 == derived:a())");//accessing Base member

Registering object instance

state["ABC"].setClass(kaguya::UserdataMetatable<ABC>()
	.setConstructors<ABC(),ABC(int)>()
	.addFunction("get_value", &ABC::value)
	.addFunction("set_value", &ABC::setValue)
	);
ABC abc(43);
//register object pointer
state["abc"] = &abc;
state("assert(43 == abc:get_value())");
//or copy instance
state["copy_abc"] = abc;
state("assert(43 == copy_abc:get_value())");
//or registering shared instance
state["shared_abc"] = kaguya::standard::shared_ptr<ABC>(new ABC(43));//kaguya::standard::shared_ptr is std::shared_ptr or boost::shared_ptr.
state("assert(43 == shared_abc:get_value())");

Object lifetime

state["Base"].setClass(kaguya::UserdataMetatable<Base>());
Base base;

//registering pointer. lifetime is same base
state["b"] = &base;
state["b"] = kaguya::standard::ref(base);

//registering copy instance. copied instance lifetime is handling in lua vm(garbage collection).
state["b"] = base;
state["b"] = static_cast<Base const&>(base);

Registering function

void c_free_standing_function(int v){std::cout <<"c_free_standing_function called:" << v << std::endl;}
state["fun"] = &c_free_standing_function;
state["fun"](54); //c_free_standing_function called:54
state("fun(22)");//c_free_standing_function called:22

state["lambda"] = kaguya::function([]{std::cout << "lambda called" << std::endl;});//C++11 lambda
state("lambda()");//lambda called


state["overload"] = kaguya::overload(
	[](int) {std::cout << "int version" << std::endl; },
	[](const std::string&) {std::cout << "string version" << std::endl; },
	[]() {std::cout << "no arg version" << std::endl; }
);
state("overload()");//no args version
state("overload(2)");//int version
state("overload('2')");//string version

Registering function with default arguments

//free function
int defargfn(int a = 3, int b = 2, int c = 1)
{
	return a*b*c;
}

KAGUYA_FUNCTION_OVERLOADS(defargfn_wrapper, defargfn,0,3)
state["defarg"] = kaguya::function(defargfn_wrapper());
state.dostring("assert(defarg() == 6)");
state.dostring("assert(defarg(6) == 12)");
state.dostring("assert(defarg(6,5) == 30)");
state.dostring("assert(defarg(2,2,2) == 8)");

//member function
struct TestClass
{
	int defargfn(int a = 3, int b = 2, int c = 1)
	{
		return a*b*c;
	}
};
KAGUYA_MEMBER_FUNCTION_OVERLOADS(defargfn_wrapper, TestClass, defargfn, 0, 3)
state["TestClass"].setClass(kaguya::UserdataMetatable<TestClass>()
	.setConstructors<TestClass()>()
	.addFunction("defarg", defargfn_wrapper())
);
state.dostring("test = TestClass.new()");
state.dostring("assert(test:defargfn() == 6)");
state.dostring("assert(test:defargfn(6) == 12)");
state.dostring("assert(test:defargfn(6,5) == 30)");
state.dostring("assert(test:defargfn(2,2,2) == 8)");

Variadic arguments function

state["va_fun"] = kaguya::function([](kaguya::VariadicArgType args) {for (auto v : args) { std::cout << v.get<std::string>() << ","; }std::cout << std::endl; });//C++11 lambda
state("va_fun(3,4,6,\"text\",6,444)");//3,4,6,text,6,444,

Multiple Results to Lua

If return type of function is tuple, it returns multiple results to Lua

state["multireturn"] = kaguya::function([]() { return std::tuple<int, int>(32, 34); });
state("print(multireturn())");//32    34

Nil values

Luas nil converts to nullptr or 0 for pointer types, can be checked for with isNilref() and is different than the integer 0. When you want to pass nil to lua either pass nullptr/(void*)0 or kaguya::NilValue.

state["value"] = kaguya::NilValue();
//or state["value"] = nullptr;
//or state["value"] = (void*) 0;
state("assert(value == nil)");
state("assert(value ~= 0)");
assert(state["value"].isNilref());
assert(state["value"] == kaguya::NilValue());
assert(state["value"] == nullptr);

state["value"] = 0;
state("assert(value ~= nil)");
state("assert(value == 0)");
assert(!state["value"].isNilref());
assert(state["value"] != kaguya::NilValue());
assert(state["value"] != nullptr);

Coroutine

kaguya::LuaThread cor = state.newThread();
state("corfun = function(arg)"
"coroutine.yield(arg) "
"coroutine.yield(arg*2) "
"coroutine.yield(arg*3) "
"return arg*4 "
" end");//define corouine function

kaguya::LuaFunction corfun = state["corfun"];//lua function get

//exec coroutine with function and argument
std::cout << int(cor(corfun, 3)) << std::endl;//3
std::cout << int(cor()) << std::endl;//6
//resume template argument is result type
std::cout << cor.resume<int>() << std::endl;//9
std::cout << int(cor()) << std::endl;//12

kaguya::LuaThread cor2 = state.newThread();
//3,6,9,12,
while(!cor2.isThreadDead())
{
	std::cout << cor2.resume<int>(corfun, 3) << ",";
}

Automatic type conversion

std::map and std::vector will be converted to a lua-table by default

kaguya::State s;
std::vector<int> vect = { 2,4,6,1 };
s["vect"] = vect;
s("print(type(vect))");// table
s("for i,v in ipairs(vect) do print(v) end");

output:

table
1 2
2 4
3 6
4 1

kaguya::State s;
std::map<std::string, int> map = { { "apple",3 },{ "dog",5 },{"cat",124},{ "catfood",644 } };
s["map"] = map;
s("print(type(map))");// table
s("for i,v in pairs(map) do print(i,v) end");

output:

table
catfood 644
dog     5
cat     124
apple   3

Type conversion customization

If you want to customize the type conversion from/to lua, specialize kaguya::lua_type_traits

example: (this is already implemented for std::string per default)

template<>  struct lua_type_traits<std::string> {
	typedef std::string get_type;
	typedef const std::string& push_type;

	static bool strictCheckType(lua_State* l, int index)
	{
		return lua_type(l, index) == LUA_TSTRING;
	}
	static bool checkType(lua_State* l, int index)
	{
		return lua_isstring(l, index) != 0;
	}
	static get_type get(lua_State* l, int index)
	{
		size_t size = 0;
		const char* buffer = lua_tolstring(l, index, &size);
		return std::string(buffer, size);
	}
	static int push(lua_State* l, push_type s)
	{
		lua_pushlstring(l, s.c_str(), s.size());
		return 1;
	}
};

Handling Errors

Encountered lua errors will be written to the console by default, but you can change this:

void HandleError(int errCode, const char * szError)
{  //customize your error handling, eg. write to file...
}
kaguya::State l;
l.setErrorHandler(HandleError);
l.dofile("./scripts/custom.lua"); // eg. accessing a non-existing file will invoke HandleError above

run test

mkdir build
cd build
cmake ..
make
ctest

If you don't want to use the default (system) library, add these 3 options to the cmake command

cmake -DLUA_INCLUDE_DIRS=path/to/lua/header/dir -DLUA_LIBRARY_DIRS=/abspath/to/lua/library/dir -DLUA_LIBRARIES=lualibname