mlua/examples/examples.rs

#[macro_use]
extern crate hlist_macro;
extern crate rlua;

use rlua::*;

fn examples() -> LuaResult<()> {
    // Create a Lua context with Lua::new().  Eventually, this will allow further control on the
    // lua std library, and will specifically allow limiting Lua to a subset of "safe"
    // functionality.

    let lua = Lua::new();

    // You can get and set global variables

    lua.set("string_var", "hello")?;
    lua.set("int_var", 42)?;

    assert_eq!(lua.get::<_, String>("string_var")?, "hello");
    assert_eq!(lua.get::<_, i64>("int_var")?, 42);

    // You can load and evaluate lua code.  The second parameter here gives the chunk a better name
    // when lua error messages are printed.

    lua.load(r#"
            global = 'foo'..'bar'
        "#,
              Some("example code"))?;
    assert_eq!(lua.get::<_, String>("global")?, "foobar");

    assert_eq!(lua.eval::<i32>("1 + 1")?, 2);
    assert_eq!(lua.eval::<bool>("false == false")?, true);
    assert_eq!(lua.eval::<i32>("return 1 + 2")?, 3);

    // You can create and manage lua tables

    let array_table = lua.create_empty_table()?;
    array_table.set(1, "one")?;
    array_table.set(2, "two")?;
    array_table.set(3, "three")?;
    assert_eq!(array_table.length()?, 3);

    let map_table = lua.create_empty_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 LuaTable back into Lua

    lua.set("array_table", array_table)?;
    lua.set("map_table", map_table)?;

    lua.eval::<()>(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
    "#)?;

    // You can load lua functions

    let print: LuaFunction = lua.get("print")?;
    print.call::<_, ()>("hello from rust")?;

    // There is a specific method for handling variadics that involves Heterogeneous Lists.  This
    // is one way to call a function with multiple parameters:

    print
        .call::<_, ()>(hlist!["hello", "again", "from", "rust"])?;

    // You can bind rust functions to lua as well

    let check_equal = lua.create_function(|lua, args| {
        // Functions wrapped in lua receive their arguments packed together as LuaMultiValue.  The
        // first thing that most wrapped functions will do is "unpack" this LuaMultiValue into its
        // parts.  Due to lifetime type signature limitations, this cannot be done automatically from the
        // function signature, but this will be fixed with ATCs.  Notice the use of the hlist
        // macros again.
        let hlist_pat![list1, list2] = lua.unpack::<HList![Vec<String>, Vec<String>]>(args)?;

        // This function just checks whether two string lists are equal, and in an inefficient way.
        // Results are returned with lua.pack, which takes any number of values and turns them back
        // into LuaMultiValue.  In this way, multiple values can also be returned to Lua.  Again,
        // this cannot be inferred as part of the function signature due to the same lifetime type
        // signature limitations.
        lua.pack(list1 == list2)
    })?;
    lua.set("check_equal", check_equal)?;

    // You can also accept variadic arguments to rust functions
    let join = lua.create_function(|lua, args| {
                                       let strings = lua.unpack::<LuaVariadic<String>>(args)?.0;
                                       // (This is quadratic!, it's just an example!)
                                       lua.pack(strings.iter().fold("".to_owned(), |a, b| a + b))
                                   })?;
    lua.set("join", join)?;

    assert_eq!(lua.eval::<bool>(r#"check_equal({"a", "b", "c"}, {"a", "b", "c"})"#)?,
               true);
    assert_eq!(lua.eval::<bool>(r#"check_equal({"a", "b", "c"}, {"d", "e", "f"})"#)?,
               false);
    assert_eq!(lua.eval::<String>(r#"join("a", "b", "c")"#)?, "abc");

    // You can create userdata with methods and metamethods defined on them.  Here's a more
    // complete example that shows all of the features of this API together

    #[derive(Copy, Clone)]
    struct Vec2(f32, f32);

    impl LuaUserDataType for Vec2 {
        fn add_methods(methods: &mut LuaUserDataMethods<Self>) {
            methods.add_method("magnitude", |lua, vec, _| {
                let mag_squared = vec.0 * vec.0 + vec.1 * vec.1;
                lua.pack(mag_squared.sqrt())
            });

            methods.add_meta_function(LuaMetaMethod::Add, |lua, params| {
                let hlist_pat![vec1, vec2] = lua.unpack::<HList![Vec2, Vec2]>(params)?;
                lua.pack(Vec2(vec1.0 + vec2.0, vec1.1 + vec2.1))
            });
        }
    }

    let vec2_constructor = lua.create_function(|lua, args| {
            let hlist_pat![x, y] = lua.unpack::<HList![f32, f32]>(args)?;
            lua.pack(Vec2(x, y))
        })?;
    lua.set("vec2", vec2_constructor)?;

    assert_eq!(lua.eval::<f32>("(vec2(1, 2) + vec2(2, 2)):magnitude()")?,
               5.0);

    Ok(())
}

fn main() {
    examples().unwrap();
}