make it so a Table can only be a normal table, or a metatable, not both at the same time

src/state.rs

@@ -173,7 +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)?)
+            Table::with_ref(self, LuaRef::from_stack(self)?, false)
         }
     }
 
@@ -297,7 +297,7 @@ impl State {
 
                 // 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
+                //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()));

src/table.rs

@@ -5,16 +5,12 @@ use mlua_sys as lua;
 
 use crate::{ensure_type, FromLuaStack, LuaRef, PushToLuaStack, Result, StackGuard, State};
 
-pub(crate) struct MetaTableInfo {
-    name: Option<String>,
-    lref: LuaRef,
-}
-
 #[derive(Clone)]
 pub struct Table<'a> {
     state: &'a State,
     pub(crate) lref: LuaRef,
-    pub(crate) meta: Option<LuaRef>, // Some if this table is a metatable
+    /// a boolean indicating if this Table is a Metatable
+    mt_marker: bool,
 }
 
 impl<'a> Table<'a> {
@@ -31,7 +27,7 @@ impl<'a> Table<'a> {
         Ok(Self {
             state,
             lref,
-            meta: None,
+            mt_marker: false,
         })
     }
 
@@ -39,16 +35,10 @@ impl<'a> Table<'a> {
         let name_term = format!("{}\0", name);
         let name_term_c = name_term.as_str().as_ptr() as *const i8;
         
-        let (lref, meta_ref) = unsafe {
+        let 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
@@ -60,23 +50,18 @@ 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            
-            (LuaRef::from_stack(state)?, meta)
+            LuaRef::from_stack(state)?
         };
         
         Ok(Self {
             state,
-            lref,
-            meta: Some(meta_ref)
+            lref: meta_ref,
+            mt_marker: true
         })
     }
 
     /// Construct a table with a lua reference to one.
-    pub fn with_ref(state: &'a State, lua_ref: LuaRef) -> Result<Self> {
+    pub fn with_ref(state: &'a State, lua_ref: LuaRef, is_metatable: bool) -> Result<Self> {
         let s = state.state_ptr();
         
         unsafe {
@@ -91,7 +76,7 @@ impl<'a> Table<'a> {
         Ok(Self {
             state,
             lref: lua_ref,
-            meta: None,
+            mt_marker: is_metatable,
         })
     }
 
@@ -107,7 +92,7 @@ impl<'a> Table<'a> {
         unsafe {
             let _g = StackGuard::new(self.state);
 
-            if let Some(_) = &self.meta {
+            if self.mt_marker {
                 self.state.ensure_stack(4)?;
             } else {
                 self.state.ensure_stack(3)?;
@@ -118,11 +103,6 @@ impl<'a> Table<'a> {
             val.push_to_lua_stack(self.state)?;
 
             lua::lua_settable(s, -3);
-
-            if let Some(mt) = &self.meta {
-                mt.push_to_lua_stack(self.state)?;
-                lua::lua_setmetatable(s, -2);
-            }
         }
 
         Ok(())
@@ -226,37 +206,27 @@ impl<'a> Table<'a> {
 
     /// Set something in the metatable
     /// 
-    /// # Panics
-    /// Panics if this table is not a metatable
+    /// Does nothing if this table is not a metatable
     pub fn set_meta<K, V>(&self, key: K, val: V) -> Result<()>
     where
         K: PushToLuaStack<'a>,
         V: PushToLuaStack<'a>
     {
-        let mt = self.meta.as_ref()
-            .expect("this table is not a meta table!");
+        if self.mt_marker {
+            unsafe {
+                let s = self.state.state_ptr();
+                self.state.ensure_stack(3)?;
+                let _g = StackGuard::new(self.state);
 
-        unsafe {
-            let s = self.state.state_ptr();
-            self.state.ensure_stack(3)?;
-            let _g = StackGuard::new(self.state);
-
-            mt.push_to_lua_stack(self.state)?;
-            key.push_to_lua_stack(self.state)?;
-            val.push_to_lua_stack(self.state)?;
-            lua::lua_settable(s, -3);
+                self.lref.push_to_lua_stack(self.state)?;
+                key.push_to_lua_stack(self.state)?;
+                val.push_to_lua_stack(self.state)?;
+                lua::lua_settable(s, -3);
+            }
         }
 
         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<'a> for Table<'a> {
@@ -271,6 +241,6 @@ impl<'a> PushToLuaStack<'a> for Table<'a> {
 impl<'a> FromLuaStack<'a> for Table<'a> {
     unsafe fn from_lua_stack(state: &'a State) -> Result<Self> {
         ensure_type(state, lua::LUA_TTABLE, -1)?;
-        Table::with_ref(state, LuaRef::from_stack(state)?)
+        Table::with_ref(state, LuaRef::from_stack(state)?, false)
     }
 }