Groundwork for userdata

Still need a way to add methods and functions

src/function.rs

@@ -1,9 +1,10 @@
 use std::ffi::CStr;
 
-use crate::{FromLuaStack, LuaRef, PushToLuaStack, StackGuard, State};
+use crate::{AsLua, FromLuaStack, LuaRef, PushToLuaStack, StackGuard, State};
 
 use mlua_sys as lua;
 
+#[derive(Clone)]
 pub struct Function<'a> {
     state: &'a State,
     lref: LuaRef
@@ -18,7 +19,7 @@ impl<'a> FromLuaStack<'a> for Function<'a> {
     }
 }
 
-impl<'a> PushToLuaStack for Function<'a> {
+impl<'a> PushToLuaStack<'a> for Function<'a> {
     unsafe fn push_to_lua_stack(&self, state: &State) -> crate::Result<()> {
         self.lref.push_to_lua_stack(state)
     }
@@ -59,20 +60,26 @@ impl<'a> Function<'a> {
     }
 }
 
+impl<'a> AsLua<'a> for Function<'a> {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<crate::Value<'a>> {
+        Ok(crate::Value::Function(self.clone()))
+    }
+}
+
 pub trait PushToLuaStackMulti<'a> {
     fn len(&self) -> usize;
-    fn push_args_to_lua_stack(&self, state: &State) -> crate::Result<()>;
+    fn push_args_to_lua_stack(&self, state: &'a State) -> crate::Result<()>;
 }
 
 impl<'a, T> PushToLuaStackMulti<'a> for T
 where
-    T: PushToLuaStack,
+    T: PushToLuaStack<'a>,
 {
     fn len(&self) -> usize {
         1
     }
 
-    fn push_args_to_lua_stack(&self, state: &State) -> crate::Result<()> {
+    fn push_args_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
         unsafe {
             self.push_to_lua_stack(state)?;
         }
@@ -109,14 +116,14 @@ impl<'a, T: FromLuaStack<'a>> FromLuaStackMulti<'a> for T {
 macro_rules! impl_function_arg_tuple {
     ( $count: expr, $first: tt, $( $name: tt ),+ ) => (
         #[allow(non_snake_case)]
-        impl<'a, $first: PushToLuaStack, $($name: PushToLuaStack,)+> PushToLuaStackMulti<'a> for ($first, $($name,)+) {
+        impl<'a, $first: PushToLuaStack<'a>, $($name: PushToLuaStack<'a>,)+> PushToLuaStackMulti<'a> for ($first, $($name,)+) {
             fn len(&self) -> usize {
                 // this will end up generating $count - 1 - 1 - 1... hopefully the compiler will
                 // optimize that out
                 $count
             }
 
-            fn push_args_to_lua_stack(&self, state: &State) -> crate::Result<()> {
+            fn push_args_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
                 let ($first, $($name,)+) = self;
         
                 unsafe {
@@ -134,7 +141,13 @@ macro_rules! impl_function_arg_tuple {
             }
         
             fn results_from_lua_stack(state: &'a State) -> crate::Result<Self> {
-                Ok(unsafe { ( $first::from_lua_stack(state)?, $( $name::from_lua_stack(state)?, )+ ) })
+                unsafe { 
+                    let ($( $name, )+ $first) = ( $( $name::from_lua_stack(state)?, )+ $first::from_lua_stack(state)? );
+
+                    Ok( ($first, $( $name, )+) )
+                }
+                //Ok(unsafe { ( $( $name::from_lua_stack(state)?, )+ $first::from_lua_stack(state)? ) })
+                //Ok(unsafe { ( $first::from_lua_stack(state)?, $( $name::from_lua_stack(state)?, )+ ) })
             }
         }
 
@@ -144,12 +157,12 @@ macro_rules! impl_function_arg_tuple {
     // implements PushToLuaStackMulti and FromLuaStackMulti for a tuple with a single element
     ( $count: expr, $only: tt ) => {
         #[allow(non_snake_case)]
-        impl<'a, $only: PushToLuaStack> PushToLuaStackMulti<'a> for ($only,) {
+        impl<'a, $only: PushToLuaStack<'a>> PushToLuaStackMulti<'a> for ($only,) {
             fn len(&self) -> usize {
                 1
             }
 
-            fn push_args_to_lua_stack(&self, state: &State) -> crate::Result<()> {
+            fn push_args_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
                 let (a,) = self;
         
                 unsafe {

src/main.rs

@@ -1,4 +1,4 @@
-use std::{ffi::CStr, str::Utf8Error, sync::Arc};
+use std::{any::type_name, ffi::CStr, marker::PhantomData, mem, ptr, str::Utf8Error, sync::Arc};
 
 use lua::{lua_typename, lua_type};
 use mlua_sys as lua;
@@ -18,29 +18,19 @@ use value::*;
 pub mod guard;
 use guard::*;
 
-/* struct RustFn {
+pub mod userdata;
-
+use userdata::*;
-} */
-
-/* struct RustFnUpvalue {
-    
-} */
-
-/// 
-pub fn ptr_to_string(ptr: *const i8) -> std::result::Result<String, Utf8Error> {
-    let c = unsafe { CStr::from_ptr(ptr) };
-    let s= c.to_str()?;
-    Ok(s.to_string())
-}
 
+pub mod util;
+use util::*;
 
 fn main() -> Result<()> {
     let lua = State::new();
-    lua.expose_libraries(&[StdLibrary::Debug]);
+    lua.expose_libraries(&[StdLibrary::Debug, StdLibrary::Package]);
 
     let globals = lua.globals()?;
 
-    let a = |lua: &State, (num,): (i32,)| -> Result<i32> {
+    let a = |_lua: &State, (num,): (i32,)| -> Result<i32> {
         println!("Rust got number from lua: {}", num);
         Ok(999)
     };
@@ -48,35 +38,8 @@ fn main() -> Result<()> {
     let f = lua.create_function(a)?;
     globals.set("native_test", f)?;
     
-    //let tbl = lua.create_table()?;
+    let ud = lua.create_userdata("Vec2", Vec2 { x: 0.0, y: 0.0})?;
-
+    globals.set("Vec2", ud)?;
-    let vec2_add = lua.create_function(|lua: &State, (a, b): (Table, Table)| -> Result<Table> {
-        let ax: i32 = a.get("x")?;
-        let ay: i32 = a.get("y")?;
-
-        let bx: i32 = b.get("x")?;
-        let by: i32 = b.get("y")?;
-
-        let rx = ax + bx;
-        let ry = ay + by;
-
-        let mt = lua.create_meta_table("Vec2")?;
-        mt.set("x", rx)?;
-        mt.set("y", ry)?;
-        Ok(mt)
-    })?;
-    
-
-    let mt = lua.create_meta_table("Vec2")?;
-    mt.set("x", 50)?;
-    mt.set("y", 50)?;
-    mt.set_meta("__add", vec2_add)?;
-    globals.set("pos1", mt)?;
-
-    let mt = lua.create_meta_table("Vec2")?;
-    mt.set("x", 25)?;
-    mt.set("y", 25)?;
-    globals.set("pos2", mt)?;
 
     let tbl = lua.create_table()?;
     tbl.set("x", 10)?;
@@ -85,6 +48,8 @@ fn main() -> Result<()> {
     globals.set("X", tbl)?;
 
     lua.execute(r#"
+        require "util"
+
         --[[function dump_table(tbl)
             for k, v in pairs(tbl) do
                 if type(v) == "table" then
@@ -123,28 +88,12 @@ fn main() -> Result<()> {
         local res = native_test(50)
         print("Lua got " .. res .. " back from rust!")
 
-        print("Pos1 is (" .. pos1.x .. ", " .. pos1.y .. ")")
+        print("Vec2: " .. dump_table(Vec2))
-        print("Pos2 is (" .. pos2.x .. ", " .. pos2.y .. ")")
+        print("Meta Vec2: " .. dump_table(getmetatable(Vec2)))
-
+        --local vec2 = Vec2.new(50, 50)
-        local add_pos = pos1 + pos2
+        print("Vec2 is (" .. Vec2.x .. ", " .. Vec2.y .. ")")
-        print("Pos1 + pos2 is (" .. add_pos.x .. ", " .. add_pos.y .. ")")
     "#).unwrap();
 
-    let num = globals.get::<_, i32>("cool_num")?;
-    assert_eq!(num, 50);
-    println!("Got number as 50!");
-
-    let num = globals.get::<_, Function>("say_number")?;
-    num.exec::<_, ()>(50)?;
-
-    let num = globals.get::<_, Function>("multiply_print")?;
-    num.exec::<_, ()>((10, 5))?;
-
-    let num = globals.get::<_, Function>("multiply_ret")?;
-    let num: i32 = num.exec::<_, i32>((10, 5))?;
-    assert_eq!(num, 50);
-    println!("Did math in lua and got 50!");
-
     unsafe {
         assert_eq!(lua::lua_gettop(lua.state_ptr()), 0); // ensure that nothing is left on the stack
     }
@@ -165,10 +114,8 @@ impl LuaRef {
     /// Creates a reference to what is at the top of the stack.
     pub unsafe fn from_stack(state: &State) -> Result<Self> {
         let s = state.state_ptr();
-        let t = lua::lua_gettop(s);
 
         let r = lua::luaL_ref(s, lua::LUA_REGISTRYINDEX);
-        let t = lua::lua_gettop(s);
         if r == lua::LUA_REFNIL {
             Err(Error::Nil)
         } else {
@@ -177,7 +124,7 @@ impl LuaRef {
     }
 }
 
-impl PushToLuaStack for LuaRef {
+impl<'a> PushToLuaStack<'a> for LuaRef {
     unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
         let s = state.state_ptr();
 
@@ -236,73 +183,89 @@ impl Error {
         let msg = format!("{}", self);
         let msg_c = msg.as_ptr() as *const i8;
         lua::luaL_error(lua, msg_c);
-        panic!("never gets here");
+        unreachable!();
     }
 }
 
 /// A result for use with lua functions
 type Result<T> = core::result::Result<T, Error>;
 
-pub trait PushToLuaStack {
+pub trait PushToLuaStack<'a> {
-    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()>;
+    unsafe fn push_to_lua_stack(&self, state: &'a State) -> Result<()>;
 }
 
 pub trait FromLuaStack<'a>: Sized {
     unsafe fn from_lua_stack(state: &'a State) -> Result<Self>;
 }
 
-/* impl<'a> FromLuaStack<'a> for () {
-    unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
-        Ok(())
-    }
-}  */
-
 /// Implements PushToLuaStack for a number
-macro_rules! impl_push_to_lua_stack_number {
+macro_rules! impl_as_lua_number {
     ($ty: ident) => {
-        impl PushToLuaStack for $ty {
+        impl<'a> AsLua<'a> for $ty {
-            unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
+            fn as_lua(&self, _lua: &'a State) -> crate::Result<Value<'a>> {
-                state.ensure_stack(1)?;
+                Ok(Value::Number(*self as f64))
-                lua::lua_pushnumber(state.state_ptr(), *self as f64);
-                Ok(())
             }
         }
+
+        impl FromLua for $ty {
+            fn from_lua(_lua: &State, val: Value) -> crate::Result<Self> {
+                match val {
+                    Value::Number(v) => Ok(v as $ty),
+                    _ => {
+                        Err(Error::UnexpectedType("Number".to_string(), val.type_name().to_string()))
+                    },
+                }
+            }
+        }
+
+        impl<'a> PushToLuaStack<'a> for $ty {
+            unsafe fn push_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
+                let v = self.as_lua(state)?;
+                v.push_to_lua_stack(state)
+            }
+        }
+        
     };
 }
 
-impl<'a> FromLuaStack<'a> for i32 {
+impl_as_lua_number!(i8);
+impl_as_lua_number!(i16);
+impl_as_lua_number!(i32);
+impl_as_lua_number!(i64);
+
+impl_as_lua_number!(u8);
+impl_as_lua_number!(u16);
+impl_as_lua_number!(u32);
+impl_as_lua_number!(u64);
+
+impl_as_lua_number!(f32);
+impl_as_lua_number!(f64);
+
+impl<'a> PushToLuaStack<'a> for String {
+    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
+        state.ensure_stack(1)?;
+
+        let s = format!("{}\0", self);
+        let cstr = s.as_ptr() as *const i8;
+        lua::lua_pushstring(state.state_ptr(), cstr);
+
+        Ok(())
+    }
+}
+
+impl<'a> FromLuaStack<'a> for String {
     unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
         let s = state.state_ptr();
 
-        if lua::lua_isnumber(s, -1) == 1 {
+        let cstr = lua::lua_tostring(s, -1);
-            let v = lua::lua_tonumber(s, -1) as i32;
         lua::lua_pop(s, 1);
-            Ok(v)
-        } else {
-            let lua_ty = lua_type(s, -1);
-            let typec = CStr::from_ptr(lua_typename(s, lua_ty));
-            let type_str = typec.to_str()
-                .expect("Type has invalid bytes!");
 
-            Err(Error::unexpected_type("Number", type_str))
+        let cstr = CStr::from_ptr(cstr);
-        }
+        Ok(cstr.to_str().unwrap().to_string())
     }
 }
 
-impl_push_to_lua_stack_number!(i8);
+impl<'a> PushToLuaStack<'a> for &str {
-impl_push_to_lua_stack_number!(i16);
-impl_push_to_lua_stack_number!(i32);
-impl_push_to_lua_stack_number!(i64);
-
-impl_push_to_lua_stack_number!(u8);
-impl_push_to_lua_stack_number!(u16);
-impl_push_to_lua_stack_number!(u32);
-impl_push_to_lua_stack_number!(u64);
-
-impl_push_to_lua_stack_number!(f32);
-impl_push_to_lua_stack_number!(f64);
-
-impl PushToLuaStack for String {
     unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
         state.ensure_stack(1)?;
 
@@ -314,13 +277,49 @@ impl PushToLuaStack for String {
     }
 }
 
-impl PushToLuaStack for &str {
+pub struct Vec2 {
-    unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
+    x: f32,
-        state.ensure_stack(1)?;
+    y: f32,
+}
 
-        let s = format!("{}\0", self);
+impl Userdata for Vec2 {
-        let cstr = s.as_ptr() as *const i8;
+    fn build<'a>(builder: &mut UserdataBuilder<'a, Vec2>) -> crate::Result<()> {
-        lua::lua_pushstring(state.state_ptr(), cstr);
+        builder.name("Vec2")
+            .field_getter("x", |_, this| Ok(this.x))
+            .field_getter("y", |_, this| Ok(this.y));
+
+        Ok(())
+    }
+}
+
+pub struct UserdataProxy<T: Userdata>(PhantomData<T>);
+
+impl<T: Userdata> UserdataProxy<T> {
+    pub fn new() -> Self {
+        Self(PhantomData)
+    }
+}
+
+impl<'a, T: Userdata> AsLua<'a> for UserdataProxy<T> {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>> {
+        todo!()
+    }
+}
+
+impl<T: Userdata> Userdata for UserdataProxy<T> {
+    fn build<'a>(builder: &mut UserdataBuilder<'a, Self>) -> crate::Result<()> {
+
+        let mut other = UserdataBuilder::<T>::new();
+        T::build(&mut other)?;
+
+        builder.name(&other.name.unwrap());
+
+        for (lbl, getters) in other.field_getters.into_iter() {
+            let wrap = |state: &State, data: &Self| {
+                Ok(())
+            };
+            builder.field_getter(&lbl, wrap);
+        }
 
         Ok(())
     }

src/state.rs

@@ -1,9 +1,15 @@
 use core::ffi;
-use std::{ffi::{CString, CStr}, mem, ptr::{self, NonNull}};
+use std::{ffi::{CString, CStr}, mem, ptr::{self, NonNull}, str::Utf8Error};
 
 use mlua_sys as lua;
 
-use crate::{lua_error_guard, Error, FromLuaStack, FromLuaStackMulti, Function, LuaRef, PushToLuaStack, PushToLuaStackMulti, Result, Table};
+use crate::{ensure_type, lua_error_guard, AnyUserdata, Error, FromLuaStack, FromLuaStackMulti, Function, LuaRef, PushToLuaStack, PushToLuaStackMulti, Result, StackGuard, Table, Userdata, UserdataBuilder, Value};
+
+pub fn ptr_to_string(ptr: *const i8) -> std::result::Result<String, Utf8Error> {
+    let c = unsafe { CStr::from_ptr(ptr) };
+    let s= c.to_str()?;
+    Ok(s.to_string())
+}
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum StdLibrary {
@@ -167,7 +173,7 @@ impl State {
         unsafe {
             let s = self.state_ptr();
             lua::lua_rawgeti(s, lua::LUA_REGISTRYINDEX, lua::LUA_RIDX_GLOBALS);
-            Table::with_ref(self, LuaRef::from_stack(self)?, None)
+            Table::with_ref(self, LuaRef::from_stack(self)?)
         }
     }
 
@@ -180,11 +186,11 @@ impl State {
             let tyname = lua::lua_typename(s, ty);
             let tyname = CStr::from_ptr(tyname);
             let tyname = tyname.to_str().unwrap();
-            println!("{}: {}", i, tyname);
+            println!("{}: {}", -(t + 1 - i), tyname);
         }
     }
 
-    pub fn create_function<'a, A, R, F>(&'a self, f: F) -> Result<Function<'a>>
+    pub fn create_function<'a, A, R, F>(&self, f: F) -> Result<Function>
     where
         A: FromLuaStackMulti<'a>,
         R: PushToLuaStackMulti<'a>,
@@ -268,4 +274,63 @@ impl State {
         }
     }
 
+    /// Create userdata
+    pub fn create_userdata<T: Userdata + 'static>(&self, name: &str, data: T) -> Result<AnyUserdata> {
+        unsafe {
+            self.ensure_stack(2)?;
+            let _g = StackGuard::new(self);
+            let s = self.state_ptr();
+
+            let ptr = lua::lua_newuserdata(s, mem::size_of::<T>()).cast::<T>();
+            ptr::write(ptr, data);
+
+            let name_cstr = format!("{}\0", name);
+            let name_cstr = name_cstr.as_str();
+            let name_cstr = name_cstr.as_ptr() as *const i8;
+
+            // attempt to get the metatable
+            lua::lua_pushstring(s, name_cstr);
+            let ty = lua::lua_rawget(s, lua::LUA_REGISTRYINDEX);
+            
+            if ty == lua::LUA_TNIL {
+                lua::lua_pop(s, 1); // remove nil
+
+                // if the metatable is not made yet, make it
+                let mt = self.create_userdata_metatable::<T>()?;
+                let mt = mt.get_metatable().unwrap(); // the table 100% has a metatable
+                mt.push_to_lua_stack(self)?;
+            } else if ty != lua::LUA_TTABLE {
+                return Err(Error::RegistryConflict(name.to_string()));
+            }
+
+            lua::lua_setmetatable(s, -2);
+
+            AnyUserdata::from_lua_stack(self)
+        }
+    }
+
+    pub(crate) fn create_userdata_metatable<'a, T: Userdata + 'static>(&'a self) -> Result<Table<'a>> {
+        let mut builder = UserdataBuilder::<T>::new();
+        T::build(&mut builder)?;
+
+        let getters = builder.field_getters;
+        let name = builder.name.unwrap();
+
+        let mt = self.create_meta_table(&name)?;
+
+        if !getters.is_empty() {
+            let index_fn = self.create_function(move |lua: &State, (ud, key): (AnyUserdata, String)| {
+                if let Some(getter) = getters.get(&key) {
+                    let r = getter(lua, Value::Userdata(ud))?;
+                    Ok(r)
+                } else {
+                    Ok(Value::Nil)
+                }
+            })?;
+
+            mt.set_meta("__index", index_fn)?;
+        }
+
+        Ok(mt)
+    }
 }

src/table.rs

@@ -3,7 +3,7 @@ use std::{ffi::CStr, ops::Deref, sync::Arc};
 
 use mlua_sys as lua;
 
-use crate::{FromLuaStack, LuaRef, PushToLuaStack, Result, StackGuard, State};
+use crate::{ensure_type, FromLuaStack, LuaRef, PushToLuaStack, Result, StackGuard, State};
 
 pub(crate) struct MetaTableInfo {
     name: Option<String>,
@@ -13,8 +13,8 @@ pub(crate) struct MetaTableInfo {
 #[derive(Clone)]
 pub struct Table<'a> {
     state: &'a State,
-    lref: LuaRef,
+    pub(crate) lref: LuaRef,
-    meta: Option<LuaRef>, // Some if this table is a metatable
+    pub(crate) meta: Option<LuaRef>, // Some if this table is a metatable
 }
 
 impl<'a> Table<'a> {
@@ -38,12 +38,17 @@ impl<'a> Table<'a> {
     pub fn new_meta_table(state: &'a State, name: &str) -> Result<Self> {
         let name_term = format!("{}\0", name);
         let name_term_c = name_term.as_str().as_ptr() as *const i8;
-        let name_term_arc = Arc::new(name_term_c);
         
         let (lref, meta_ref) = unsafe {
             let _g = StackGuard::new(state);
             state.ensure_stack(2)?;
 
+            // create the table, this will be retrieved from
+            // stack after the metatable is created
+            let s = state.state_ptr();
+            lua::lua_newtable(s);
+            //let table_idx = lua::lua_gettop(s);
+
             let s = state.state_ptr();
             if lua::luaL_newmetatable(s, name_term_c) == 0 {
                 // lua::luaL_getmetatable does not return the type that was
@@ -55,11 +60,11 @@ impl<'a> Table<'a> {
                     return Err(crate::Error::RegistryConflict(name.to_string()));
                 }
             }
+            lua::lua_pushvalue(s, lua::lua_gettop(s));
+            lua::lua_setmetatable(s, -3); // -3 here since the metatable was added twice
             let meta = LuaRef::from_stack(state)?;
             
-
+            // retrieve the table created before the metatable            
-            let s = state.state_ptr();
-            lua::lua_newtable(s);
             (LuaRef::from_stack(state)?, meta)
         };
         
@@ -71,7 +76,7 @@ impl<'a> Table<'a> {
     }
 
     /// Construct a table with a lua reference to one.
-    pub fn with_ref(state: &'a State, lua_ref: LuaRef, name: Option<String>) -> Result<Self> {
+    pub fn with_ref(state: &'a State, lua_ref: LuaRef) -> Result<Self> {
         let s = state.state_ptr();
         
         unsafe {
@@ -79,7 +84,7 @@ impl<'a> Table<'a> {
             
             lua_ref.push_to_lua_stack(state)?;
             if lua::lua_istable(s, -1) == 0 {
-                panic!("Index is not a table")
+                panic!("Provided reference is not a table")
             }
         }
 
@@ -95,8 +100,8 @@ impl<'a> Table<'a> {
     /// This may trigger the `__newindex` metamethod, see [`Table::raw_set`]
     pub fn set<K, V>(&self, key: K, val: V) -> Result<()>
     where
-        K: PushToLuaStack,
+        K: PushToLuaStack<'a>,
-        V: PushToLuaStack
+        V: PushToLuaStack<'a>
     {
         let s = self.state.state_ptr();
         unsafe {
@@ -126,9 +131,9 @@ impl<'a> Table<'a> {
     /// Get a value from the table.
     /// 
     /// This may trigger the `__index` metamethod, see [`Table::raw_get`]
-    pub fn get<K, V>(&'a self, key: K) -> Result<V>
+    pub fn get<K, V>(&self, key: K) -> Result<V>
     where
-        K: PushToLuaStack,
+        K: PushToLuaStack<'a>,
         V: FromLuaStack<'a>,
     {
         let s = self.state.state_ptr();
@@ -167,8 +172,8 @@ impl<'a> Table<'a> {
     /// Set a key to a value in the table without calling any meta methods.
     pub fn raw_set<K, V>(&self, key: K, val: V) -> Result<()>
     where
-        K: PushToLuaStack,
+        K: PushToLuaStack<'a>,
-        V: PushToLuaStack
+        V: PushToLuaStack<'a>
     {
         let s = self.state.state_ptr();
         unsafe {
@@ -189,7 +194,7 @@ impl<'a> Table<'a> {
     /// Get a value from the table without calling any meta methods.
     pub fn raw_get<K, V>(&'a self, key: K) -> Result<V>
     where
-        K: PushToLuaStack,
+        K: PushToLuaStack<'a>,
         V: FromLuaStack<'a>,
     {
         let s = self.state.state_ptr();
@@ -219,10 +224,14 @@ impl<'a> Table<'a> {
         }
     }
 
+    /// Set something in the metatable
+    /// 
+    /// # Panics
+    /// Panics if this table is not a metatable
     pub fn set_meta<K, V>(&self, key: K, val: V) -> Result<()>
     where
-        K: PushToLuaStack,
+        K: PushToLuaStack<'a>,
-        V: PushToLuaStack
+        V: PushToLuaStack<'a>
     {
         let mt = self.meta.as_ref()
             .expect("this table is not a meta table!");
@@ -232,7 +241,6 @@ impl<'a> Table<'a> {
             self.state.ensure_stack(3)?;
             let _g = StackGuard::new(self.state);
 
-            //lua::luaL_getmetatable(s, **cname);
             mt.push_to_lua_stack(self.state)?;
             key.push_to_lua_stack(self.state)?;
             val.push_to_lua_stack(self.state)?;
@@ -241,9 +249,17 @@ impl<'a> Table<'a> {
 
         Ok(())
     }
+
+    /// Returns a handle to the metatable of this table
+    pub fn get_metatable(&self) -> Option<Table> {
+        self.meta.clone()
+            .map(|r| 
+                Table::with_ref(self.state, r).unwrap()
+            )
+    }
 }
 
-impl<'a> PushToLuaStack for Table<'a> {
+impl<'a> PushToLuaStack<'a> for Table<'a> {
     unsafe fn push_to_lua_stack(&self, state: &State) -> Result<()> {
         // no need to ensure stack, the LuaRef does it for us
         self.lref.push_to_lua_stack(state)?;
@@ -254,19 +270,7 @@ impl<'a> PushToLuaStack for Table<'a> {
 
 impl<'a> FromLuaStack<'a> for Table<'a> {
     unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
-        let s = state.state_ptr();
+        ensure_type(state, lua::LUA_TTABLE, -1)?;
-
+        Table::with_ref(state, LuaRef::from_stack(state)?)
-        let ty = lua::lua_type(s, -1);
-        if ty == lua::LUA_TTABLE {
-            let t = Table::with_ref(state, LuaRef::from_stack(state)?, None);
-            
-            t
-        } else {
-            let tyname = lua::lua_typename(s, ty);
-            let cstr = CStr::from_ptr(tyname);
-            let s = cstr.to_str()
-                .expect("Lua type has invalid bytes!");
-            Err(crate::Error::UnexpectedType("Table".to_string(), s.to_string()))
-        }
     }
 }

src/userdata.rs

@@ -0,0 +1,164 @@
+use std::{collections::HashMap, marker::PhantomData, sync::Arc};
+
+use crate::{ensure_type, AsLua, FromLua, FromLuaStack, LuaRef, PushToLuaStack, State, Table, Value};
+
+use mlua_sys as lua;
+
+//pub type FieldSetter<T> = fn(lua: &State, this: &T);
+//pub type FieldGetter<T, U> = fn(lua: &State, this: &T, val: &U);
+
+pub trait FieldSetter {
+    fn set_field(&self, val: Value);
+}
+
+pub trait FieldGetter {
+    fn get_field(&self) -> Value;
+}
+
+type UserdataFn<'a> = Box<dyn Fn(&'a State, Value<'a>) -> crate::Result<Value<'a>>>;
+
+pub struct UserdataBuilder<'a, T> {
+    pub(crate) name: Option<String>,
+    pub(crate) field_getters: HashMap<String, UserdataFn<'a>>,
+    _marker: PhantomData<T>,
+}
+
+impl<'a, T> UserdataBuilder<'a, T> {
+    pub fn new() -> Self {
+        Self {
+            name: None,
+            field_getters: HashMap::new(),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn name(&mut self, name: &str) -> &mut Self {
+        self.name = Some(name.to_string());
+        self
+    }
+
+    pub fn field_getter<F, R>(&mut self, name: &str, f: F) -> &mut Self
+    where
+        F: Fn(&'a State, &T) -> crate::Result<R> + 'static,
+        R: AsLua<'a>,
+    {
+        let wrap = move |lua: &'a State, val: Value<'a>| {
+            let this = val.as_userdata().unwrap(); // if this panics, its a bug
+            let this = this.as_ref::<T>()?;
+            f(lua, this).and_then(|r| r.as_lua(lua))
+        };
+        self.field_getters.insert(name.to_string(), Box::new(wrap));
+
+        self
+    }
+
+    pub fn into_meta_table(self, state: &'a State, table: &Table<'a>) -> crate::Result<()> {
+        //let this: Self = unsafe { std::mem::transmute(self) };
+        //let getters = *self.field_getters;
+        
+        /* let index_fn = state.create_function(move |lua: &'a State, (ud, key): (AnyUserdata<'a>, String)| {
+            let ud_ref = ud.as_ref::<T>()?;
+
+            if let Some(getter) = self.field_getters.get(&key) {
+                let r = getter(lua, ome(ud_ref), Value::Nil)?;
+
+                let r = unsafe { std::mem::transmute(r) };
+
+                Ok(r)
+            } else {
+                //ud.get::<_, Value<'a>>(key)
+                Ok(Value::Nil)
+            }
+        })?;
+
+        table.set("__index", index_fn)?; */
+
+        Ok(())
+    }
+
+    /* pub fn wrap_builder<U, F>(this: &mut UserdataBuilder<'a, T>, other: UserdataBuilder<'a, U>, to_proxied: F)
+    where
+        F: Fn(&'a T) -> &'a U + 'a,
+    {
+        let to_proxied = Arc::new(to_proxied);
+        for (lbl, getter) in other.field_getters.into_iter() {
+            let to_proxied_cl = to_proxied.clone();
+            let new_getter = move |lua: &'a State, this: Option<&T>, val: Value<'a>| {
+                let proxy = this.map(|t| to_proxied_cl(t));
+                getter(lua, proxy, val)
+            };
+            this.field_getters.insert(lbl, Box::new(new_getter));
+        }
+    } */
+
+    /* pub fn into_userdata(self, state: &'a State, data: T) -> crate::Result<Table<'a>> {
+        let name = self.name
+            .expect("No name was set for userdata!");
+
+        let getters = self.field_getters.clone();
+        let index_fn = state.create_function(move |lua: &'a State, (ud, key): (AnyUserdata<'a>, String)| {
+            let ud_ref = ud.as_ref::<T>()?;
+
+            if let Some(getter) = getters.get(&key) {
+                getter(lua, Some(ud_ref), Value::Nil)
+            } else {
+                //ud.get::<_, Value<'a>>(key)
+                Ok(Value::Nil)
+            }
+
+            //todo!()
+        })?;
+
+        let mt = state.create_meta_table(&name)?;
+        mt.set("__index", index_fn)?;
+
+        Ok(mt)
+    } */
+}
+
+pub trait Userdata: Sized {
+    fn build<'a>(builder: &mut UserdataBuilder<'a, Self>) -> crate::Result<()>;
+}
+
+/// A handle to some userdata on the stack
+#[derive(Clone)]
+pub struct AnyUserdata<'a> {
+    lref: LuaRef,
+    state: &'a State,
+}
+
+impl<'a> AnyUserdata<'a> {
+    pub fn from_ref(state: &'a State, lref: LuaRef) -> Self {
+        Self {
+            lref,
+            state,
+        }
+    }
+
+    pub fn as_ref<T>(&self) -> crate::Result<&'a T> {
+        unsafe {
+            let s = self.state.state_ptr();
+
+            self.lref.push_to_lua_stack(self.state)?;
+            let cptr = lua::lua_touserdata(s, -1);
+            Ok(cptr.cast::<T>().as_ref().unwrap())
+        }
+    }
+}
+
+impl<'a> FromLuaStack<'a> for AnyUserdata<'a> {
+    unsafe fn from_lua_stack(state: &'a State) -> crate::Result<Self> {
+        ensure_type(state, lua::LUA_TUSERDATA, -1)?;
+
+        Ok(AnyUserdata {
+            lref: LuaRef::from_stack(state)?,
+            state,
+        })
+    }
+}
+
+impl<'a> PushToLuaStack<'a> for AnyUserdata<'a> {
+    unsafe fn push_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
+        self.lref.push_to_lua_stack(state)
+    }
+}

src/util.rs

@@ -0,0 +1,29 @@
+use std::ffi::CStr;
+
+use crate::State;
+
+use mlua_sys as lua;
+
+pub unsafe fn ensure_type(state: &State, typ: i32, idx: i32) -> crate::Result<()> {
+    let s = state.state_ptr();
+
+    let lua_type = lua::lua_type(s, idx);
+    
+    if lua_type == typ {
+        Ok(())
+    } else {
+        let exp_tyname = lua::lua_typename(s, typ);
+        let exp_cstr = CStr::from_ptr(exp_tyname);
+        let exp_s = exp_cstr.to_str()
+            .expect("Lua type has invalid bytes!");
+
+        let tyname = lua::lua_typename(s, lua_type);
+        let cstr = CStr::from_ptr(tyname);
+        let s = cstr.to_str()
+            .expect("Lua type has invalid bytes!");
+
+        println!("ty = {}, typ = {}", lua_type, typ);
+
+        Err(crate::Error::UnexpectedType(exp_s.to_string(), s.to_string()))
+    }
+}

src/value.rs

@@ -1,19 +1,54 @@
-use crate::{Function, Table, PushToLuaStack};
+use std::ffi::CStr;
+
+use crate::{AnyUserdata, FromLuaStack, Function, PushToLuaStack, State, Table};
 
 use mlua_sys as lua;
 
+#[derive(Clone)]
 pub enum Value<'a> {
+    Nil,
     Number(f64),
     String(String),
     Function(Function<'a>),
     Table(Table<'a>),
+    Userdata(AnyUserdata<'a>),
 }
 
-impl<'a> PushToLuaStack for Value<'a> {
+impl<'a> Value<'a> {
+    pub fn is_nil(&self) -> bool {
+        matches!(self, Value::Nil)
+    }
+
+    pub fn type_name(&self) -> &'static str {
+        match self {
+            Value::Nil => "Nil",
+            Value::Number(_) => "Number",
+            Value::String(_) => "String",
+            Value::Function(_) => "Function",
+            Value::Table(_) => "Table",
+            Value::Userdata(_) => todo!(),
+        }
+    }
+
+    pub fn as_userdata(&self) -> crate::Result<&AnyUserdata> {
+        match self {
+            Value::Userdata(ud) => Ok(ud),
+            _ => {
+                Err(crate::Error::UnexpectedType("Userdata".to_string(), self.type_name().to_string()))
+            }
+        }
+    }
+}
+
+impl<'a> PushToLuaStack<'a> for Value<'a> {
     unsafe fn push_to_lua_stack(&self, state: &crate::State) -> crate::Result<()> {
         let s = state.state_ptr();
 
         match self {
+            Value::Nil => {
+                state.ensure_stack(1)?;
+                lua::lua_pushnil(s);
+            }
             Value::Number(n) => {
                 state.ensure_stack(1)?;
                 lua::lua_pushnumber(s, *n);
@@ -25,14 +60,91 @@ impl<'a> PushToLuaStack for Value<'a> {
                 let cstr = s.as_ptr() as *const i8;
                 lua::lua_pushstring(state.state_ptr(), cstr);
             }
-            Value::Function(f) => {
+            Value::Function(f) => f.push_to_lua_stack(state)?,
-                f.push_to_lua_stack(state)?;
+            Value::Table(t) => t.push_to_lua_stack(state)?,
-            },
+            Value::Userdata(ud) => ud.push_to_lua_stack(state)?,
-            Value::Table(t) => {
-                t.push_to_lua_stack(state)?;
-            }
         }
 
         Ok(())
     }
 }
+
+impl<'a> FromLuaStack<'a> for Value<'a> {
+    unsafe fn from_lua_stack(state: &'a State) -> crate::Result<Self> {
+
+        let s = state.state_ptr();
+        let ty = lua::lua_type(s, -1);
+
+        let val = match ty {
+            lua::LUA_TNIL => {
+                lua::lua_pop(s, 1);
+                
+                Ok(Value::Nil)
+            },
+            lua::LUA_TNUMBER => {
+                let n = lua::lua_tonumber(s, -1);
+                lua::lua_pop(s, 1);
+
+                Ok(Value::Number(n))
+            }
+            lua::LUA_TSTRING => {
+                let cstr = lua::lua_tostring(s, -1);
+                lua::lua_pop(s, 1);
+
+                let cstr = CStr::from_ptr(cstr);
+                let lua_str = cstr.to_str().unwrap().to_string();
+                Ok(Value::String(lua_str))
+            },
+            lua::LUA_TFUNCTION => {
+                Function::from_lua_stack(state)
+                    .map(|f| Value::Function(f))
+            },
+            lua::LUA_TTABLE => {
+                Table::from_lua_stack(state)
+                    .map(|t| Value::Table(t))
+            },
+            _ => {
+                let s = lua::lua_typename(s, ty);
+                let s = CStr::from_ptr(s);
+                let s = s.to_str().unwrap();
+                unimplemented!("Not yet able to get '{}' as a value from the stack", s);
+            }
+        };
+
+        val
+    }
+}
+
+pub trait AsLua<'a> {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>>;
+}
+
+pub trait FromLua: Sized {
+    fn from_lua(lua: &State, val: Value) -> crate::Result<Self>;
+}
+
+/* impl<'a> AsLua<'a> for Value<'a> {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>> {
+        Ok(self.clone())
+    }
+} */
+
+/* impl<'a, T: AsLua<'a>> PushToLuaStack<'a> for T {
+    unsafe fn push_to_lua_stack(&self, state: &'a State) -> crate::Result<()> {
+        let v = self.as_lua(state)?;
+        v.push_to_lua_stack(state)
+    }
+}
+ */
+impl<'a, T: FromLua> FromLuaStack<'a> for T {
+    unsafe fn from_lua_stack(state: &'a State) -> crate::Result<Self> {
+        let v = Value::from_lua_stack(state)?;
+        T::from_lua(state, v)
+    }
+}
+
+impl<'a> AsLua<'a> for () {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>> {
+        Ok(Value::Nil)
+    }
+}

util.lua

@@ -0,0 +1,50 @@
+---
+---Print a formatted string. Put `{}` where you want something to be formatted in its place.
+---
+---```lua
+---local yummy_food = "chips"
+---printf("Lets eat {} together!", yummy_food)
+---```
+---
+---The items provided in the variable arguments must implement `tostring`!
+---
+---@param str string
+---@param ...   any
+function printf(str, ...)
+    local fleft, fright = str:find("{}")
+    local formatted = ""
+    -- current vararg index
+    local arg = 1
+
+    while (fleft ~= nil and fright ~= nil) do
+        formatted = formatted .. str:sub(0, fleft - 1)
+        formatted = formatted .. tostring(select(arg, ...))
+
+        str = str:sub(fright + 1, str:len())
+
+        fleft, fright = str:find("{}")
+        arg = arg + 1
+    end
+
+    formatted = formatted .. str
+    print(formatted)
+end
+
+---
+---Recursively dumps a table as a string.
+---
+---@param obj table
+---@return string
+---@nodiscard
+function dump_table(obj)
+    if type(obj) == 'table' then
+        local s = '{ '
+        for k,v in pairs(obj) do
+            if type(k) ~= 'number' then k = '"'..k..'"' end
+            s = s .. '['..k..'] = ' .. dump_table(v) .. ','
+        end
+        return s .. '} '
+    else
+        return tostring(obj)
+    end
+end