Stack Interaction

Luwra provides several easy ways to interact with the Lua virtual stack.

Pushing Values

To get values onto the stack, use push.

luwra::push(state, 1337);

luwra::push(state, 13.37);

luwra::push(state, "Hello World");

luwra::push(state, MyUserType("Hello", 5));

You can also push them all at once.

luwra::push(state, 1337, 13.37, "Hello World", MyUserType("Hello", 5));

Reading Values

Reading values works with read. Assuming the stack has been prepared as it has been in the previous section, you can extract the values like so.

int i = luwra::read<int>(state, 1);

double d = luwra::read<double>(state, 2);

std::string s = luwra::read<std::string>(state, 3);

MyUserType& u = luwra::read<MyUserType>(state, 4);

You can also let C++ infer the types for you.

int i = luwra::read(state, 1);

double d = luwra::read(state, 2);

std::string s = luwra::read(state, 3);

MyUserType& u = luwra::read(state, 4);

Note: Type inference does not work with every compiler. Particularly GCC before version 4.9.2 is affected by this problem.

Invoke Callables with Stack Values

apply is a function that retrieves values from the stack in order to invoke a given Callable. The types of values on the stack are deduced from the parameter types to the Callable.

std::string substring(const std::string& str, size_t len) {
    return str.substr(0, len);
}

luwra::push(state, "Hello World");
luwra::push(state, 5);

// Retrieve values and invoke 'substring'.
std::string result = luwra::apply(state, 1, substring);

// This is essentially equal to the following.
std::string result = substring(luwra::read(state, 1), luwra::read(state, 2));

// You can also provide your own arguments before the stack values.
std::string result = luwra::apply(state, 2, substring, "My Own String");

// Alternatively
std::string result = substring("My Own String", luwra::read(state, 2));

If you wish to return the result of your function to the stack, simply use map.

luwra::map(state, 1, substring);
std::string result = luwra::read(state, -1);

You can also provide function objects or lambdas to apply and map.

std::string result = luwra::apply(state, 1, [](const std::string& str, size_t len) {
    return str.substr(0, len);
});