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hlua

This library is a high-level binding for Lua 5.2. You don't have access to the Lua stack, all you can do is read/write variables (including callbacks) and execute Lua code.

How to install it?

Add this to the Cargo.toml file of your project

[dependencies]
hlua = "0.3"

How to use it?

extern crate hlua;
use hlua::Lua;

The Lua struct is the main element of this library. It represents a context in which you can execute Lua code.

let mut lua = Lua::new();     // mutable is mandatory

You can check the documentation here.

Reading and writing variables

lua.set("x", 2);
lua.execute::<()>("x = x + 1").unwrap();
let x: i32 = lua.get("x").unwrap();  // x is equal to 3

Reading and writing global variables of the Lua context can be done with set and get. The get function returns an Option<T> and does a copy of the value.

The base types that can be read and written are: i8, i16, i32, u8, u16, u32, f32, f64, bool, String. &str can be written but not read.

If you wish so, you can also add other types by implementing the Push and LuaRead traits.

Executing Lua

let x: u32 = lua.execute("return 6 * 2;").unwrap();    // equals 12

The execute function takes a &str and returns a Result<T, ExecutionError> where T: LuaRead.

You can also call execute_from_reader which takes a std::io::Read as parameter. For example you can easily execute the content of a file like this:

lua.execute_from_reader::<()>(File::open(&Path::new("script.lua")).unwrap())

Writing functions

In order to write a function, you must wrap it around hlua::functionX where X is the number of parameters. This is for the moment a limitation of Rust's inferrence system.

fn add(a: i32, b: i32) -> i32 {
    a + b
}

lua.set("add", hlua::function2(add));
lua.execute::<()>("local c = add(2, 4)");   // calls the `add` function above
let c: i32 = lua.get("c").unwrap();   // returns 6

In Lua, functions are exactly like regular variables.

You can write regular functions as well as closures:

lua.set("mul", hlua::function2(|a: i32, b: i32| a * b));

Note that the lifetime of the Lua context must be equal to or shorter than the lifetime of closures. This is enforced at compile-time.

let mut a = 5i;

{
    let mut lua = Lua::new();

    lua.set("inc", || a += 1);    // borrows 'a'
    for i in (0 .. 15) {
        lua.execute::<()>("inc()").unwrap();
    }
} // unborrows `a`

assert_eq!(a, 20)

Error handling

If your Rust function returns a Result object which contains an error, then a Lua error will be triggered.

Manipulating Lua tables

Manipulating a Lua table can be done by reading a LuaTable object. This can be achieved easily by reading a LuaTable object.

let mut table: hlua::LuaTable<_> = lua.get("a").unwrap();

You can then iterate through the table with the .iter() function. Note that the value returned by the iterator is an Option<(Key, Value)>, the Option being empty when either the key or the value is not convertible to the requested type. The filter_map function (provided by the standard Iterator trait) is very useful when dealing with this.

for (key, value) in table.iter().filter_map(|e| e) {
    ...
}

You can also retreive and modify individual indices:

let x = table.get("a").unwrap();
table.set("b", "hello");

Calling Lua functions

You can call Lua functions by reading a functions_read::LuaFunction.

lua.execute::<()>("
    function get_five() 
        return 5
    end");

let get_five: hlua::LuaFunction<_> = lua.get("get_five").unwrap();
let value: i32 = get_five.call().unwrap();
assert_eq!(value, 5);

This object holds a mutable reference of Lua, so you can't read or modify anything in the Lua context while the get_five variable exists. It is not possible to store the function for the moment, but it may be in the future.

Reading and writing Rust containers

(note: not yet possible to read all containers, see below)

It is possible to read and write whole Rust containers at once:

lua.set("a", [ 12, 13, 14, 15 ]);
let hashmap: HashMap<i32, f64> = [1., 2., 3.].into_iter().enumerate().map(|(k, v)| (k as i32, *v as f64)).collect();
lua.set("v", hashmap);

If the container has single elements, then the indices will be numerical. For example in the code above, the 12 will be at index 1, the 13 at index 2, etc.

If the container has tuples of two elements, then the first one will be considered as the key and the second one as the value.

This can be useful to create APIs:

fn foo() { }
fn bar() { }

lua.set("mylib", [
    ("foo", hlua::function0(foo)),
    ("bar", hlua::function0(bar))
]);

lua.execute::<()>("mylib.foo()");

It is possible to read a Vec<AnyLuaValue>:

        let mut lua = Lua::new();

        lua.execute::<()>(r#"v = { 1, 2, 3 }"#).unwrap();

        let read: Vec<_> = lua.get("v").unwrap();
        assert_eq!(
            read,
            [1., 2., 3.].iter()
                .map(|x| AnyLuaValue::LuaNumber(*x)).collect::<Vec<_>>());

In case table represents sparse array, has non-numeric keys, or indices not starting at 1, .get() will return None, as Rust's Vec doesn't support these features.

It is possible to read a HashMap<AnyHashableLuaValue, AnyLuaValue>:

let mut lua = Lua::new();

lua.execute::<()>(r#"v = { [-1] = -1, ["foo"] = 2, [2.] = 42 }"#).unwrap();

let read: HashMap<_, _> = lua.get("v").unwrap();
assert_eq!(read[&AnyHashableLuaValue::LuaNumber(-1)], AnyLuaValue::LuaNumber(-1.));
assert_eq!(read[&AnyHashableLuaValue::LuaString("foo".to_owned())], AnyLuaValue::LuaNumber(2.));
assert_eq!(read[&AnyHashableLuaValue::LuaNumber(2)], AnyLuaValue::LuaNumber(42.));
assert_eq!(read.len(), 3);

User data

(note: the API here is very unstable for the moment)

When you expose functions to Lua, you may wish to read or write more elaborate objects. This is called a user data.

To do so, you should implement the Push, CopyRead and ConsumeRead for your types. This is usually done by redirecting the call to userdata::push_userdata.

struct Foo;

impl<L> hlua::Push<L> for Foo where L: hlua::AsMutLua<'lua> {
    fn push_to_lua(self, lua: L) -> hlua::PushGuard<L> {
        lua::userdata::push_userdata(self, lua,
            |mut metatable| {
                // you can define all the member functions of Foo here
                // see the official Lua documentation for metatables
                metatable.set("__call", hlua::function0(|| println!("hello from foo")))
            })
    }
}

fn main() {
    let mut lua = lua::Lua::new();
    lua.set("foo", Foo);
    lua.execute::<()>("foo()");       // prints "hello from foo"
}

Contributing

Contributions are welcome!