use std::f32; use std::iter::FromIterator; use mlua::{Function, Lua, MetaMethod, Result, UserData, UserDataMethods, Variadic}; fn main() -> Result<()> { // You can create a new Lua state with `Lua::new()`. This loads the default Lua std library // *without* the debug library. let lua = Lua::new(); // You can get and set global variables. Notice that the globals table here is a permanent // reference to _G, and it is mutated behind the scenes as Lua code is loaded. This API is // based heavily around sharing and internal mutation (just like Lua itself). let globals = lua.globals(); globals.set("string_var", "hello")?; globals.set("int_var", 42)?; assert_eq!(globals.get::<_, String>("string_var")?, "hello"); assert_eq!(globals.get::<_, i64>("int_var")?, 42); // You can load and evaluate Lua code. The returned type of `Lua::load` is a builder // that allows you to change settings before running Lua code. Here, we are using it to set // the name of the laoded chunk to "example code", which will be used when Lua error // messages are printed. lua.load( r#" global = 'foo'..'bar' "#, ) .set_name("example code")? .exec()?; assert_eq!(globals.get::<_, String>("global")?, "foobar"); assert_eq!(lua.load("1 + 1").eval::()?, 2); assert_eq!(lua.load("false == false").eval::()?, true); assert_eq!(lua.load("return 1 + 2").eval::()?, 3); // You can create and manage Lua tables let array_table = lua.create_table()?; array_table.set(1, "one")?; array_table.set(2, "two")?; array_table.set(3, "three")?; assert_eq!(array_table.len()?, 3); let map_table = lua.create_table()?; map_table.set("one", 1)?; map_table.set("two", 2)?; map_table.set("three", 3)?; let v: i64 = map_table.get("two")?; assert_eq!(v, 2); // You can pass values like `Table` back into Lua globals.set("array_table", array_table)?; globals.set("map_table", map_table)?; lua.load( r#" for k, v in pairs(array_table) do print(k, v) end for k, v in pairs(map_table) do print(k, v) end "#, ) .exec()?; // You can load Lua functions let print: Function = globals.get("print")?; print.call::<_, ()>("hello from rust")?; // This API generally handles variadics using tuples. This is one way to call a function with // multiple parameters: print.call::<_, ()>(("hello", "again", "from", "rust"))?; // But, you can also pass variadic arguments with the `Variadic` type. print.call::<_, ()>(Variadic::from_iter( ["hello", "yet", "again", "from", "rust"].iter().cloned(), ))?; // You can bind rust functions to Lua as well. Callbacks receive the Lua state inself as their // first parameter, and the arguments given to the function as the second parameter. The type // of the arguments can be anything that is convertible from the parameters given by Lua, in // this case, the function expects two string sequences. let check_equal = lua.create_function(|_, (list1, list2): (Vec, Vec)| { // This function just checks whether two string lists are equal, and in an inefficient way. // Lua callbacks return `mlua::Result`, an Ok value is a normal return, and an Err return // turns into a Lua 'error'. Again, any type that is convertible to Lua may be returned. Ok(list1 == list2) })?; globals.set("check_equal", check_equal)?; // You can also accept runtime variadic arguments to rust callbacks. let join = lua.create_function(|_, strings: Variadic| { // (This is quadratic!, it's just an example!) Ok(strings.iter().fold("".to_owned(), |a, b| a + b)) })?; globals.set("join", join)?; assert_eq!( lua.load(r#"check_equal({"a", "b", "c"}, {"a", "b", "c"})"#) .eval::()?, true ); assert_eq!( lua.load(r#"check_equal({"a", "b", "c"}, {"d", "e", "f"})"#) .eval::()?, false ); assert_eq!(lua.load(r#"join("a", "b", "c")"#).eval::()?, "abc"); // Callbacks receive a Lua state as their first parameter so that they can use it to // create new Lua values, if necessary. let create_table = lua.create_function(|lua, ()| { let t = lua.create_table()?; t.set(1, 1)?; t.set(2, 2)?; Ok(t) })?; globals.set("create_table", create_table)?; assert_eq!(lua.load(r#"create_table()[2]"#).eval::()?, 2); // You can create userdata with methods and metamethods defined on them. // Here's a worked example that shows many of the features of this API // together #[derive(Copy, Clone)] struct Vec2(f32, f32); impl UserData for Vec2 { fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) { methods.add_method("magnitude", |_, vec, ()| { let mag_squared = vec.0 * vec.0 + vec.1 * vec.1; Ok(mag_squared.sqrt()) }); methods.add_meta_function(MetaMethod::Add, |_, (vec1, vec2): (Vec2, Vec2)| { Ok(Vec2(vec1.0 + vec2.0, vec1.1 + vec2.1)) }); } } let vec2_constructor = lua.create_function(|_, (x, y): (f32, f32)| Ok(Vec2(x, y)))?; globals.set("vec2", vec2_constructor)?; assert!( (lua.load("(vec2(1, 2) + vec2(2, 2)):magnitude()") .eval::()? - 5.0) .abs() < f32::EPSILON ); // Normally, Rust types passed to `Lua` must be `'static`, because there is no way to be // sure of their lifetime inside the Lua state. There is, however, a limited way to lift this // requirement. You can call `Lua::scope` to create userdata and callbacks types that only live // for as long as the call to scope, but do not have to be `'static` (and `Send`). { let mut rust_val = 0; lua.scope(|scope| { // We create a 'sketchy' Lua callback that holds a mutable reference to the variable // `rust_val`. Outside of a `Lua::scope` call, this would not be allowed // because it could be unsafe. lua.globals().set( "sketchy", scope.create_function_mut(|_, ()| { rust_val = 42; Ok(()) })?, )?; lua.load("sketchy()").exec() })?; assert_eq!(rust_val, 42); } // We were able to run our 'sketchy' function inside the scope just fine. However, if we // try to run our 'sketchy' function outside of the scope, the function we created will have // been invalidated and we will generate an error. If our function wasn't invalidated, we // might be able to improperly access the freed `rust_val` which would be unsafe. assert!(lua.load("sketchy()").exec().is_err()); Ok(()) }