## tlua

This library is a high-level binding for [Tarantool](https://github.com/tarantool/tarantool) LuaJIT. It is fork of
[hlua](https://github.com/tomaka/hlua) library improved and modified to work with Tarantool LuaJIT ABI.

### How to use it?

```rust
use tlua::Lua;
```

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

```rust
let lua = Lua::new();
```

**[You can check the documentation here](https://docs.rs/tlua)**.

#### Reading and writing variables

```rust
lua.set("x", 2);
lua.exec("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

```rust
lua.exec("a = 2");
let x: u32 = lua.eval("return 6 * a;").unwrap();    // equals 12
```

The `exec` function takes a `&str` and returns `Result<(), LuaError>`.
The `eval` function takes a `&str` and returns a `Result<T, LuaError>`
where `T: LuaRead`.

You can also call `exec_from`/`eval_from` which take a `std::io::Read` as
parameter.
For example you can easily execute the content of a file like this:

```rust
lua.exec_from(File::open(&Path::new("script.lua")).unwrap())
```

#### Writing functions

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

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

lua.set("add", tlua::function2(add));
lua.exec("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:

```rust
lua.set("mul", tlua::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.

```rust
let mut a = 5i;

{
    let lua = Lua::new();

    lua.set("inc", || a += 1);    // borrows 'a'
    for i in (0 .. 15) {
        lua.exec("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.

```rust
let table: tlua::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.

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

You can also retreive and modify individual indices:

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

#### Calling Lua functions

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

```rust
lua.exec("
    function get_five() 
        return 5
    end");

let get_five: tlua::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:

```rust
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:

```rust
fn foo() { }
fn bar() { }

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

lua.exec("mylib.foo()");
```

It is possible to read a `Vec<AnyLuaValue>`:

```rust
        let lua = Lua::new();

        lua.exec(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>`:

```rust
let lua = Lua::new();

lua.exec(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`.

```rust
struct Foo;

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

fn main() {
    let lua = lua::Lua::new();
    lua.set("foo", Foo);
    lua.exec("foo()");       // prints "hello from foo"
}
```