diff --git a/Cargo.toml b/Cargo.toml
index 395c5c6..4107d6c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -33,6 +33,7 @@ lua53 = []
 lua52 = []
 lua51 = []
 luajit = []
+luajit52 = ["luajit"]
 vendored = ["lua-src", "luajit-src"]
 module = ["mlua_derive"]
 async = ["futures-core", "futures-task", "futures-util"]
@@ -45,6 +46,7 @@ mlua_derive = { version = "=0.6.0", optional = true, path = "mlua_derive" }
 bstr = { version = "0.2", features = ["std"], default_features = false }
 once_cell = { version = "1.0" }
 num-traits = { version = "0.2.14" }
+rustc-hash = "1.0"
 futures-core = { version = "0.3.5", optional = true }
 futures-task = { version = "0.3.5", optional = true }
 futures-util = { version = "0.3.5", optional = true }
@@ -55,7 +57,7 @@ erased-serde = { version = "0.3", optional = true }
 cc = { version = "1.0" }
 pkg-config = { version = "0.3.17" }
 lua-src = { version = ">= 540.0.0, < 550.0.0", optional = true }
-luajit-src = { version = ">= 210.1.2, < 220.0.0", optional = true }
+luajit-src = { version = ">= 210.3.1, < 220.0.0", optional = true }
 
 [dev-dependencies]
 rustyline = "8.0"
diff --git a/README.md b/README.md
index 4bf5df4..68a7b71 100644
--- a/README.md
+++ b/README.md
@@ -33,6 +33,7 @@ Below is a list of the available feature flags. By default `mlua` does not enabl
 * `lua52`: activate Lua [5.2] support
 * `lua51`: activate Lua [5.1] support
 * `luajit`: activate [LuaJIT] support
+* `luajit52`: activate [LuaJIT] support with partial compatibility with Lua 5.2
 * `vendored`: build static Lua(JIT) library from sources during `mlua` compilation using [lua-src] or [luajit-src] crates
 * `module`: enable module mode (building loadable `cdylib` library for Lua)
 * `async`: enable async/await support (any executor can be used, eg. [tokio] or [async-std])
diff --git a/build/find_vendored.rs b/build/find_vendored.rs
index 25ed510..46b87d3 100644
--- a/build/find_vendored.rs
+++ b/build/find_vendored.rs
@@ -10,7 +10,13 @@ pub fn probe_lua() -> PathBuf {
     #[cfg(feature = "lua51")]
     let artifacts = lua_src::Build::new().build(lua_src::Lua51);
     #[cfg(feature = "luajit")]
-    let artifacts = luajit_src::Build::new().build();
+    let artifacts = {
+        let mut builder = luajit_src::Build::new();
+        if cfg!(feature = "luajit52") {
+            builder.lua52compat(true);
+        }
+        builder.build()
+    };
 
     #[cfg(not(feature = "module"))]
     artifacts.print_cargo_metadata();
diff --git a/build/main.rs b/build/main.rs
index c17f11c..833766d 100644
--- a/build/main.rs
+++ b/build/main.rs
@@ -201,7 +201,9 @@ fn main() {
         feature = "lua51",
         feature = "luajit"
     )))]
-    compile_error!("You must enable one of the features: lua54, lua53, lua52, lua51, luajit");
+    compile_error!(
+        "You must enable one of the features: lua54, lua53, lua52, lua51, luajit, luajit52"
+    );
 
     #[cfg(all(
         feature = "lua54",
@@ -212,19 +214,27 @@ fn main() {
             feature = "luajit"
         )
     ))]
-    compile_error!("You can enable only one of the features: lua54, lua53, lua52, lua51, luajit");
+    compile_error!(
+        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52"
+    );
 
     #[cfg(all(
         feature = "lua53",
         any(feature = "lua52", feature = "lua51", feature = "luajit")
     ))]
-    compile_error!("You can enable only one of the features: lua54, lua53, lua52, lua51, luajit");
+    compile_error!(
+        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52"
+    );
 
     #[cfg(all(feature = "lua52", any(feature = "lua51", feature = "luajit")))]
-    compile_error!("You can enable only one of the features: lua54, lua53, lua52, lua51, luajit");
+    compile_error!(
+        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52"
+    );
 
     #[cfg(all(feature = "lua51", feature = "luajit"))]
-    compile_error!("You can enable only one of the features: lua54, lua53, lua52, lua51, luajit");
+    compile_error!(
+        "You can enable only one of the features: lua54, lua53, lua52, lua51, luajit, luajit52"
+    );
 
     // We don't support "vendored module" mode on windows
     #[cfg(all(feature = "vendored", feature = "module", target_os = "windows"))]
diff --git a/src/conversion.rs b/src/conversion.rs
index 6da46c7..d4c589f 100644
--- a/src/conversion.rs
+++ b/src/conversion.rs
@@ -2,6 +2,7 @@
 
 use std::borrow::Cow;
 use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
+use std::convert::TryInto;
 use std::ffi::{CStr, CString};
 use std::hash::{BuildHasher, Hash};
 use std::string::String as StdString;
@@ -348,18 +349,15 @@ macro_rules! lua_convert_int {
     ($x:ty) => {
         impl<'lua> ToLua<'lua> for $x {
             fn to_lua(self, _: &'lua Lua) -> Result<Value<'lua>> {
-                if let Some(i) = cast(self) {
-                    Ok(Value::Integer(i))
-                } else {
-                    // TODO: Remove conversion to Number in v0.7
-                    cast(self)
-                        .ok_or_else(|| Error::ToLuaConversionError {
-                            from: stringify!($x),
-                            to: "number",
-                            message: Some("out of range".to_owned()),
-                        })
-                        .map(Value::Number)
-                }
+                cast(self)
+                    .map(Value::Integer)
+                    .or_else(|| cast(self).map(Value::Number))
+                    // This is impossible error because conversion to Number never fails
+                    .ok_or_else(|| Error::ToLuaConversionError {
+                        from: stringify!($x),
+                        to: "number",
+                        message: Some("out of range".to_owned()),
+                    })
             }
         }
 
@@ -451,37 +449,36 @@ where
     }
 }
 
-macro_rules! lua_convert_array {
-    ($($N:literal)+) => {
-        $(
-            impl<'lua, T> ToLua<'lua> for [T; $N]
-            where
-                T: Clone + ToLua<'lua>,
-            {
-                fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
-                    (&self).to_lua(lua)
-                }
-            }
-
-            impl<'lua, T> ToLua<'lua> for &[T; $N]
-            where
-                T: Clone + ToLua<'lua>,
-            {
-                fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
-                    Ok(Value::Table(
-                        lua.create_sequence_from(self.iter().cloned())?,
-                    ))
-                }
-            }
-        )+
+impl<'lua, T, const N: usize> ToLua<'lua> for [T; N]
+where
+    T: ToLua<'lua>,
+{
+    fn to_lua(self, lua: &'lua Lua) -> Result<Value<'lua>> {
+        Ok(Value::Table(lua.create_sequence_from(self)?))
     }
 }
 
-lua_convert_array! {
-    0  1  2  3  4  5  6  7  8  9
-   10 11 12 13 14 15 16 17 18 19
-   20 21 22 23 24 25 26 27 28 29
-   30 31 32
+impl<'lua, T, const N: usize> FromLua<'lua> for [T; N]
+where
+    T: FromLua<'lua>,
+{
+    fn from_lua(value: Value<'lua>, _: &'lua Lua) -> Result<Self> {
+        if let Value::Table(table) = value {
+            let vec = table.sequence_values().collect::<Result<Vec<_>>>()?;
+            vec.try_into()
+                .map_err(|vec: Vec<T>| Error::FromLuaConversionError {
+                    from: "Table",
+                    to: "Array",
+                    message: Some(format!("expected table of length {}, got {}", N, vec.len())),
+                })
+        } else {
+            Err(Error::FromLuaConversionError {
+                from: value.type_name(),
+                to: "Array",
+                message: Some("expected table".to_string()),
+            })
+        }
+    }
 }
 
 impl<'lua, T: ToLua<'lua>> ToLua<'lua> for Box<[T]> {
diff --git a/src/ffi/lua.rs b/src/ffi/lua.rs
index 9244559..a48be1a 100644
--- a/src/ffi/lua.rs
+++ b/src/ffi/lua.rs
@@ -23,6 +23,7 @@
 
 //! Contains definitions from `lua.h`.
 
+use std::marker::{PhantomData, PhantomPinned};
 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
 use std::os::raw::c_uchar;
 use std::os::raw::{c_char, c_int, c_void};
@@ -81,7 +82,11 @@ pub const LUA_ERRERR: c_int = 5;
 pub const LUA_ERRERR: c_int = 6;
 
 /// A raw Lua state associated with a thread.
-pub type lua_State = c_void;
+#[repr(C)]
+pub struct lua_State {
+    _data: [u8; 0],
+    _marker: PhantomData<(*mut u8, PhantomPinned)>,
+}
 
 // basic types
 pub const LUA_TNONE: c_int = -1;
@@ -621,7 +626,7 @@ extern "C" {
 #[cfg(any(feature = "lua54", feature = "lua53"))]
 #[inline(always)]
 pub unsafe fn lua_getextraspace(L: *mut lua_State) -> *mut c_void {
-    L.offset(-super::glue::LUA_EXTRASPACE as isize) as *mut c_void
+    (L as *mut c_char).offset(-super::glue::LUA_EXTRASPACE as isize) as *mut c_void
 }
 
 #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
diff --git a/src/lua.rs b/src/lua.rs
index 4a255f8..d20c7d1 100644
--- a/src/lua.rs
+++ b/src/lua.rs
@@ -1,4 +1,4 @@
-use std::any::TypeId;
+use std::any::{Any, TypeId};
 use std::cell::{Ref, RefCell, RefMut, UnsafeCell};
 use std::collections::HashMap;
 use std::ffi::CString;
@@ -9,6 +9,8 @@ use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe, Location};
 use std::sync::{Arc, Mutex, RwLock};
 use std::{mem, ptr, str};
 
+use rustc_hash::FxHashMap;
+
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::function::Function;
@@ -63,10 +65,12 @@ pub struct Lua {
 
 // Data associated with the Lua.
 struct ExtraData {
-    registered_userdata: HashMap<TypeId, c_int>,
-    registered_userdata_mt: HashMap<*const c_void, Option<TypeId>>,
+    registered_userdata: FxHashMap<TypeId, c_int>,
+    registered_userdata_mt: FxHashMap<*const c_void, Option<TypeId>>,
     registry_unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
 
+    app_data: RefCell<HashMap<TypeId, Box<dyn Any>>>,
+
     libs: StdLib,
     mem_info: Option<Box<MemoryInfo>>,
     safe: bool, // Same as in the Lua struct
@@ -456,9 +460,10 @@ impl Lua {
         // Create ExtraData
 
         let extra = Arc::new(UnsafeCell::new(ExtraData {
-            registered_userdata: HashMap::new(),
-            registered_userdata_mt: HashMap::new(),
+            registered_userdata: FxHashMap::default(),
+            registered_userdata_mt: FxHashMap::default(),
             registry_unref_list: Arc::new(Mutex::new(Some(Vec::new()))),
+            app_data: RefCell::new(HashMap::new()),
             ref_thread,
             libs: StdLib::NONE,
             mem_info: None,
@@ -1577,6 +1582,74 @@ impl Lua {
         }
     }
 
+    /// Sets or replaces an application data object of type `T`.
+    ///
+    /// Application data could be accessed at any time by using [`Lua::app_data_ref()`] or [`Lua::app_data_mut()`]
+    /// methods where `T` is the data type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use mlua::{Lua, Result};
+    ///
+    /// fn hello(lua: &Lua, _: ()) -> Result<()> {
+    ///     let mut s = lua.app_data_mut::<&str>().unwrap();
+    ///     assert_eq!(*s, "hello");
+    ///     *s = "world";
+    ///     Ok(())
+    /// }
+    ///
+    /// fn main() -> Result<()> {
+    ///     let lua = Lua::new();
+    ///     lua.set_app_data("hello");
+    ///     lua.create_function(hello)?.call(())?;
+    ///     let s = lua.app_data_ref::<&str>().unwrap();
+    ///     assert_eq!(*s, "world");
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn set_app_data<T: 'static + MaybeSend>(&self, data: T) {
+        let extra = unsafe { &mut (*self.extra.get()) };
+        extra
+            .app_data
+            .try_borrow_mut()
+            .expect("cannot borrow mutably app data container")
+            .insert(TypeId::of::<T>(), Box::new(data));
+    }
+
+    /// Gets a reference to an application data object stored by [`Lua::set_app_data()`] of type `T`.
+    pub fn app_data_ref<T: 'static>(&self) -> Option<Ref<T>> {
+        let extra = unsafe { &(*self.extra.get()) };
+        let app_data = extra
+            .app_data
+            .try_borrow()
+            .expect("cannot borrow app data container");
+        let value = app_data.get(&TypeId::of::<T>())?.downcast_ref::<T>()? as *const _;
+        Some(Ref::map(app_data, |_| unsafe { &*value }))
+    }
+
+    /// Gets a mutable reference to an application data object stored by [`Lua::set_app_data()`] of type `T`.
+    pub fn app_data_mut<T: 'static>(&self) -> Option<RefMut<T>> {
+        let extra = unsafe { &(*self.extra.get()) };
+        let mut app_data = extra
+            .app_data
+            .try_borrow_mut()
+            .expect("cannot mutably borrow app data container");
+        let value = app_data.get_mut(&TypeId::of::<T>())?.downcast_mut::<T>()? as *mut _;
+        Some(RefMut::map(app_data, |_| unsafe { &mut *value }))
+    }
+
+    /// Removes an application data of type `T`.
+    pub fn remove_app_data<T: 'static>(&self) -> Option<T> {
+        let extra = unsafe { &mut (*self.extra.get()) };
+        extra
+            .app_data
+            .try_borrow_mut()
+            .expect("cannot mutably borrow app data container")
+            .remove(&TypeId::of::<T>())
+            .and_then(|data| data.downcast().ok().map(|data| *data))
+    }
+
     // Uses 2 stack spaces, does not call checkstack
     pub(crate) unsafe fn push_value(&self, value: Value) -> Result<()> {
         match value {
@@ -1769,11 +1842,18 @@ impl Lua {
 
         // Prepare metatable, add meta methods first and then meta fields
         let metatable_nrec = methods.meta_methods.len() + fields.meta_fields.len();
+        #[cfg(feature = "async")]
+        let metatable_nrec = metatable_nrec + methods.async_meta_methods.len();
         push_table(self.state, 0, metatable_nrec as c_int)?;
         for (k, m) in methods.meta_methods {
             self.push_value(Value::Function(self.create_callback(m)?))?;
             rawset_field(self.state, -2, k.validate()?.name())?;
         }
+        #[cfg(feature = "async")]
+        for (k, m) in methods.async_meta_methods {
+            self.push_value(Value::Function(self.create_async_callback(m)?))?;
+            rawset_field(self.state, -2, k.validate()?.name())?;
+        }
         for (k, f) in fields.meta_fields {
             self.push_value(f(self)?)?;
             rawset_field(self.state, -2, k.validate()?.name())?;
@@ -1807,10 +1887,9 @@ impl Lua {
         }
 
         let mut methods_index = None;
-        #[cfg(feature = "async")]
-        let methods_nrec = methods.methods.len() + methods.async_methods.len();
-        #[cfg(not(feature = "async"))]
         let methods_nrec = methods.methods.len();
+        #[cfg(feature = "async")]
+        let methods_nrec = methods_nrec + methods.async_methods.len();
         if methods_nrec > 0 {
             push_table(self.state, 0, methods_nrec as c_int)?;
             for (k, m) in methods.methods {
@@ -2425,7 +2504,7 @@ impl<'lua, T: AsRef<[u8]> + ?Sized> AsChunk<'lua> for T {
 }
 
 // Creates required entries in the metatable cache (see `util::METATABLE_CACHE`)
-pub(crate) fn init_metatable_cache(cache: &mut HashMap<TypeId, u8>) {
+pub(crate) fn init_metatable_cache(cache: &mut FxHashMap<TypeId, u8>) {
     cache.insert(TypeId::of::<Arc<UnsafeCell<ExtraData>>>(), 0);
     cache.insert(TypeId::of::<Callback>(), 0);
     cache.insert(TypeId::of::<CallbackUpvalue>(), 0);
@@ -2712,6 +2791,8 @@ struct StaticUserDataMethods<'lua, T: 'static + UserData> {
     #[cfg(feature = "async")]
     async_methods: Vec<(Vec<u8>, AsyncCallback<'lua, 'static>)>,
     meta_methods: Vec<(MetaMethod, Callback<'lua, 'static>)>,
+    #[cfg(feature = "async")]
+    async_meta_methods: Vec<(MetaMethod, AsyncCallback<'lua, 'static>)>,
     _type: PhantomData<T>,
 }
 
@@ -2722,6 +2803,8 @@ impl<'lua, T: 'static + UserData> Default for StaticUserDataMethods<'lua, T> {
             #[cfg(feature = "async")]
             async_methods: Vec::new(),
             meta_methods: Vec::new(),
+            #[cfg(feature = "async")]
+            async_meta_methods: Vec::new(),
             _type: PhantomData,
         }
     }
@@ -2821,6 +2904,20 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
             .push((meta.into(), Self::box_method_mut(method)));
     }
 
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    fn add_async_meta_method<S, A, R, M, MR>(&mut self, meta: S, method: M)
+    where
+        T: Clone,
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + MaybeSend + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'lua + Future<Output = Result<R>>,
+    {
+        self.async_meta_methods
+            .push((meta.into(), Self::box_async_method(method)));
+    }
+
     fn add_meta_function<S, A, R, F>(&mut self, meta: S, function: F)
     where
         S: Into<MetaMethod>,
@@ -2843,6 +2940,19 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
             .push((meta.into(), Self::box_function_mut(function)));
     }
 
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    fn add_async_meta_function<S, A, R, F, FR>(&mut self, meta: S, function: F)
+    where
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + MaybeSend + Fn(&'lua Lua, A) -> FR,
+        FR: 'lua + Future<Output = Result<R>>,
+    {
+        self.async_meta_methods
+            .push((meta.into(), Self::box_async_function(function)));
+    }
+
     // Below are internal methods used in generated code
 
     fn add_callback(&mut self, name: Vec<u8>, callback: Callback<'lua, 'static>) {
@@ -2857,6 +2967,15 @@ impl<'lua, T: 'static + UserData> UserDataMethods<'lua, T> for StaticUserDataMet
     fn add_meta_callback(&mut self, meta: MetaMethod, callback: Callback<'lua, 'static>) {
         self.meta_methods.push((meta, callback));
     }
+
+    #[cfg(feature = "async")]
+    fn add_async_meta_callback(
+        &mut self,
+        meta: MetaMethod,
+        callback: AsyncCallback<'lua, 'static>,
+    ) {
+        self.async_meta_methods.push((meta, callback))
+    }
 }
 
 impl<'lua, T: 'static + UserData> StaticUserDataMethods<'lua, T> {
@@ -3202,6 +3321,10 @@ macro_rules! lua_userdata_impl {
                 for (meta, callback) in orig_methods.meta_methods {
                     methods.add_meta_callback(meta, callback);
                 }
+                #[cfg(feature = "async")]
+                for (meta, callback) in orig_methods.async_meta_methods {
+                    methods.add_async_meta_callback(meta, callback);
+                }
             }
         }
     };
diff --git a/src/scope.rs b/src/scope.rs
index 3b1a93e..79ce558 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -693,6 +693,21 @@ impl<'lua, T: UserData> UserDataMethods<'lua, T> for NonStaticUserDataMethods<'l
         ));
     }
 
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    fn add_async_meta_method<S, A, R, M, MR>(&mut self, _meta: S, _method: M)
+    where
+        T: Clone,
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + MaybeSend + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'lua + Future<Output = Result<R>>,
+    {
+        // The panic should never happen as async non-static code wouldn't compile
+        // Non-static lifetime must be bounded to 'lua lifetime
+        mlua_panic!("asynchronous meta methods are not supported for non-static userdata")
+    }
+
     fn add_meta_function<S, A, R, F>(&mut self, meta: S, function: F)
     where
         S: Into<MetaMethod>,
@@ -722,6 +737,20 @@ impl<'lua, T: UserData> UserDataMethods<'lua, T> for NonStaticUserDataMethods<'l
             })),
         ));
     }
+
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    fn add_async_meta_function<S, A, R, F, FR>(&mut self, _meta: S, _function: F)
+    where
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + MaybeSend + Fn(&'lua Lua, A) -> FR,
+        FR: 'lua + Future<Output = Result<R>>,
+    {
+        // The panic should never happen as async non-static code wouldn't compile
+        // Non-static lifetime must be bounded to 'lua lifetime
+        mlua_panic!("asynchronous meta functions are not supported for non-static userdata")
+    }
 }
 
 struct NonStaticUserDataFields<'lua, T: UserData> {
diff --git a/src/serde/de.rs b/src/serde/de.rs
index c77ca44..bda7f24 100644
--- a/src/serde/de.rs
+++ b/src/serde/de.rs
@@ -1,9 +1,9 @@
 use std::cell::RefCell;
-use std::collections::HashSet;
 use std::os::raw::c_void;
 use std::rc::Rc;
 use std::string::String as StdString;
 
+use rustc_hash::FxHashSet;
 use serde::de::{self, IntoDeserializer};
 
 use crate::error::{Error, Result};
@@ -16,7 +16,7 @@ use crate::value::Value;
 pub struct Deserializer<'lua> {
     value: Value<'lua>,
     options: Options,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
 }
 
 /// A struct with options to change default deserializer behavior.
@@ -45,23 +45,23 @@ pub struct Options {
 
 impl Default for Options {
     fn default() -> Self {
-        Options {
-            deny_unsupported_types: true,
-            deny_recursive_tables: true,
-        }
+        Self::new()
     }
 }
 
 impl Options {
     /// Returns a new instance of `Options` with default parameters.
-    pub fn new() -> Self {
-        Self::default()
+    pub const fn new() -> Self {
+        Options {
+            deny_unsupported_types: true,
+            deny_recursive_tables: true,
+        }
     }
 
     /// Sets [`deny_unsupported_types`] option.
     ///
     /// [`deny_unsupported_types`]: #structfield.deny_unsupported_types
-    pub fn deny_unsupported_types(mut self, enabled: bool) -> Self {
+    pub const fn deny_unsupported_types(mut self, enabled: bool) -> Self {
         self.deny_unsupported_types = enabled;
         self
     }
@@ -86,14 +86,14 @@ impl<'lua> Deserializer<'lua> {
         Deserializer {
             value,
             options,
-            visited: Rc::new(RefCell::new(HashSet::new())),
+            visited: Rc::new(RefCell::new(FxHashSet::default())),
         }
     }
 
     fn from_parts(
         value: Value<'lua>,
         options: Options,
-        visited: Rc<RefCell<HashSet<*const c_void>>>,
+        visited: Rc<RefCell<FxHashSet<*const c_void>>>,
     ) -> Self {
         Deserializer {
             value,
@@ -313,7 +313,7 @@ impl<'lua, 'de> serde::Deserializer<'de> for Deserializer<'lua> {
 struct SeqDeserializer<'lua> {
     seq: TableSequence<'lua, Value<'lua>>,
     options: Options,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
 }
 
 impl<'lua, 'de> de::SeqAccess<'de> for SeqDeserializer<'lua> {
@@ -351,7 +351,7 @@ struct MapDeserializer<'lua> {
     pairs: TablePairs<'lua, Value<'lua>, Value<'lua>>,
     value: Option<Value<'lua>>,
     options: Options,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
     processed: usize,
 }
 
@@ -407,7 +407,7 @@ struct EnumDeserializer<'lua> {
     variant: StdString,
     value: Option<Value<'lua>>,
     options: Options,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
 }
 
 impl<'lua, 'de> de::EnumAccess<'de> for EnumDeserializer<'lua> {
@@ -431,7 +431,7 @@ impl<'lua, 'de> de::EnumAccess<'de> for EnumDeserializer<'lua> {
 struct VariantDeserializer<'lua> {
     value: Option<Value<'lua>>,
     options: Options,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
 }
 
 impl<'lua, 'de> de::VariantAccess<'de> for VariantDeserializer<'lua> {
@@ -499,12 +499,12 @@ impl<'lua, 'de> de::VariantAccess<'de> for VariantDeserializer<'lua> {
 // Used to track recursive tables but allow to traverse same tables multiple times
 struct RecursionGuard {
     ptr: *const c_void,
-    visited: Rc<RefCell<HashSet<*const c_void>>>,
+    visited: Rc<RefCell<FxHashSet<*const c_void>>>,
 }
 
 impl RecursionGuard {
     #[inline]
-    fn new(table: &Table, visited: &Rc<RefCell<HashSet<*const c_void>>>) -> Self {
+    fn new(table: &Table, visited: &Rc<RefCell<FxHashSet<*const c_void>>>) -> Self {
         let visited = Rc::clone(visited);
         let lua = table.0.lua;
         let ptr =
@@ -524,7 +524,7 @@ impl Drop for RecursionGuard {
 fn check_value_if_skip(
     value: &Value,
     options: Options,
-    visited: &RefCell<HashSet<*const c_void>>,
+    visited: &RefCell<FxHashSet<*const c_void>>,
 ) -> Result<bool> {
     match value {
         Value::Table(table) => {
diff --git a/src/serde/ser.rs b/src/serde/ser.rs
index e0371e1..c6155ae 100644
--- a/src/serde/ser.rs
+++ b/src/serde/ser.rs
@@ -52,24 +52,24 @@ pub struct Options {
 
 impl Default for Options {
     fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Options {
+    /// Returns a new instance of [`Options`] with default parameters.
+    pub const fn new() -> Self {
         Options {
             set_array_metatable: true,
             serialize_none_to_null: true,
             serialize_unit_to_null: true,
         }
     }
-}
-
-impl Options {
-    /// Returns a new instance of [`Options`] with default parameters.
-    pub fn new() -> Self {
-        Self::default()
-    }
 
     /// Sets [`set_array_metatable`] option.
     ///
     /// [`set_array_metatable`]: #structfield.set_array_metatable
-    pub fn set_array_metatable(mut self, enabled: bool) -> Self {
+    pub const fn set_array_metatable(mut self, enabled: bool) -> Self {
         self.set_array_metatable = enabled;
         self
     }
@@ -77,7 +77,7 @@ impl Options {
     /// Sets [`serialize_none_to_null`] option.
     ///
     /// [`serialize_none_to_null`]: #structfield.serialize_none_to_null
-    pub fn serialize_none_to_null(mut self, enabled: bool) -> Self {
+    pub const fn serialize_none_to_null(mut self, enabled: bool) -> Self {
         self.serialize_none_to_null = enabled;
         self
     }
@@ -85,7 +85,7 @@ impl Options {
     /// Sets [`serialize_unit_to_null`] option.
     ///
     /// [`serialize_unit_to_null`]: #structfield.serialize_unit_to_null
-    pub fn serialize_unit_to_null(mut self, enabled: bool) -> Self {
+    pub const fn serialize_unit_to_null(mut self, enabled: bool) -> Self {
         self.serialize_unit_to_null = enabled;
         self
     }
diff --git a/src/userdata.rs b/src/userdata.rs
index f6bc0e6..877f2da 100644
--- a/src/userdata.rs
+++ b/src/userdata.rs
@@ -102,7 +102,13 @@ pub enum MetaMethod {
     /// This is not an operator, but it will be called by the built-in `pairs` function.
     ///
     /// Requires `feature = "lua54/lua53/lua52"`
-    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52", doc))]
+    #[cfg(any(
+        feature = "lua54",
+        feature = "lua53",
+        feature = "lua52",
+        feature = "luajit52",
+        doc
+    ))]
     Pairs,
     /// The `__ipairs` metamethod.
     ///
@@ -111,7 +117,7 @@ pub enum MetaMethod {
     /// Requires `feature = "lua52"`
     ///
     /// [`ipairs`]: https://www.lua.org/manual/5.2/manual.html#pdf-ipairs
-    #[cfg(any(feature = "lua52", doc))]
+    #[cfg(any(feature = "lua52", feature = "luajit52", doc))]
     IPairs,
     /// The `__close` metamethod.
     ///
@@ -188,9 +194,14 @@ impl MetaMethod {
             MetaMethod::Call => "__call",
             MetaMethod::ToString => "__tostring",
 
-            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+            #[cfg(any(
+                feature = "lua54",
+                feature = "lua53",
+                feature = "lua52",
+                feature = "luajit52"
+            ))]
             MetaMethod::Pairs => "__pairs",
-            #[cfg(feature = "lua52")]
+            #[cfg(any(feature = "lua52", feature = "luajit52"))]
             MetaMethod::IPairs => "__ipairs",
 
             #[cfg(feature = "lua54")]
@@ -250,9 +261,14 @@ impl From<StdString> for MetaMethod {
             "__call" => MetaMethod::Call,
             "__tostring" => MetaMethod::ToString,
 
-            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+            #[cfg(any(
+                feature = "lua54",
+                feature = "lua53",
+                feature = "lua52",
+                feature = "luajit52"
+            ))]
             "__pairs" => MetaMethod::Pairs,
-            #[cfg(feature = "lua52")]
+            #[cfg(any(feature = "lua52", feature = "luajit52"))]
             "__ipairs" => MetaMethod::IPairs,
 
             #[cfg(feature = "lua54")]
@@ -395,6 +411,25 @@ pub trait UserDataMethods<'lua, T: UserData> {
         R: ToLuaMulti<'lua>,
         M: 'static + MaybeSend + FnMut(&'lua Lua, &mut T, A) -> Result<R>;
 
+    /// Add an async metamethod which accepts a `T` as the first parameter and returns Future.
+    /// The passed `T` is cloned from the original value.
+    ///
+    /// This is an async version of [`add_meta_method`].
+    ///
+    /// Requires `feature = "async"`
+    ///
+    /// [`add_meta_method`]: #method.add_meta_method
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    fn add_async_meta_method<S, A, R, M, MR>(&mut self, name: S, method: M)
+    where
+        T: Clone,
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        M: 'static + MaybeSend + Fn(&'lua Lua, T, A) -> MR,
+        MR: 'lua + Future<Output = Result<R>>;
+
     /// Add a metamethod which accepts generic arguments.
     ///
     /// Metamethods for binary operators can be triggered if either the left or right argument to
@@ -419,6 +454,23 @@ pub trait UserDataMethods<'lua, T: UserData> {
         R: ToLuaMulti<'lua>,
         F: 'static + MaybeSend + FnMut(&'lua Lua, A) -> Result<R>;
 
+    /// Add a metamethod which accepts generic arguments and returns Future.
+    ///
+    /// This is an async version of [`add_meta_function`].
+    ///
+    /// Requires `feature = "async"`
+    ///
+    /// [`add_meta_function`]: #method.add_meta_function
+    #[cfg(all(feature = "async", not(feature = "lua51")))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
+    fn add_async_meta_function<S, A, R, F, FR>(&mut self, name: S, function: F)
+    where
+        S: Into<MetaMethod>,
+        A: FromLuaMulti<'lua>,
+        R: ToLuaMulti<'lua>,
+        F: 'static + MaybeSend + Fn(&'lua Lua, A) -> FR,
+        FR: 'lua + Future<Output = Result<R>>;
+
     //
     // Below are internal methods used in generated code
     //
@@ -432,6 +484,15 @@ pub trait UserDataMethods<'lua, T: UserData> {
 
     #[doc(hidden)]
     fn add_meta_callback(&mut self, _meta: MetaMethod, _callback: Callback<'lua, 'static>) {}
+
+    #[doc(hidden)]
+    #[cfg(feature = "async")]
+    fn add_async_meta_callback(
+        &mut self,
+        _meta: MetaMethod,
+        _callback: AsyncCallback<'lua, 'static>,
+    ) {
+    }
 }
 
 /// Field registry for [`UserData`] implementors.
@@ -758,7 +819,6 @@ impl<'lua> AnyUserData<'lua> {
 
     /// Takes out the value of `UserData` and sets the special "destructed" metatable that prevents
     /// any further operations with this userdata.
-    #[doc(hidden)]
     pub fn take<T: 'static + UserData>(&self) -> Result<T> {
         let lua = self.0.lua;
         unsafe {
diff --git a/src/util.rs b/src/util.rs
index 6a4c923..c028758 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,5 +1,4 @@
 use std::any::{Any, TypeId};
-use std::collections::HashMap;
 use std::error::Error as StdError;
 use std::fmt::Write;
 use std::os::raw::{c_char, c_int, c_void};
@@ -8,12 +7,13 @@ use std::sync::Arc;
 use std::{mem, ptr, slice};
 
 use once_cell::sync::Lazy;
+use rustc_hash::FxHashMap;
 
 use crate::error::{Error, Result};
 use crate::ffi;
 
-static METATABLE_CACHE: Lazy<HashMap<TypeId, u8>> = Lazy::new(|| {
-    let mut map = HashMap::with_capacity(32);
+static METATABLE_CACHE: Lazy<FxHashMap<TypeId, u8>> = Lazy::new(|| {
+    let mut map = FxHashMap::with_capacity_and_hasher(32, Default::default());
     crate::lua::init_metatable_cache(&mut map);
     map.insert(TypeId::of::<WrappedFailure>(), 0);
     map.insert(TypeId::of::<String>(), 0);
@@ -842,9 +842,14 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
         "__newindex",
         "__call",
         "__tostring",
-        #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+        #[cfg(any(
+            feature = "lua54",
+            feature = "lua53",
+            feature = "lua52",
+            feature = "luajit52"
+        ))]
         "__pairs",
-        #[cfg(any(feature = "lua53", feature = "lua52"))]
+        #[cfg(any(feature = "lua53", feature = "lua52", feature = "luajit52"))]
         "__ipairs",
         #[cfg(feature = "lua54")]
         "__close",
diff --git a/tests/async.rs b/tests/async.rs
index aa9a5b7..21762de 100644
--- a/tests/async.rs
+++ b/tests/async.rs
@@ -3,7 +3,7 @@
 use std::cell::Cell;
 use std::rc::Rc;
 use std::sync::{
-    atomic::{AtomicI64, Ordering},
+    atomic::{AtomicI64, AtomicU64, Ordering},
     Arc,
 };
 use std::time::Duration;
@@ -12,7 +12,8 @@ use futures_timer::Delay;
 use futures_util::stream::TryStreamExt;
 
 use mlua::{
-    Error, Function, Lua, Result, Table, TableExt, Thread, UserData, UserDataMethods, Value,
+    Error, Function, Lua, MetaMethod, Result, Table, TableExt, Thread, UserData, UserDataMethods,
+    Value,
 };
 
 #[tokio::test]
@@ -276,7 +277,7 @@ async fn test_async_table() -> Result<()> {
 #[tokio::test]
 async fn test_async_userdata() -> Result<()> {
     #[derive(Clone)]
-    struct MyUserData(Arc<AtomicI64>);
+    struct MyUserData(Arc<AtomicU64>);
 
     impl UserData for MyUserData {
         fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
@@ -295,13 +296,20 @@ async fn test_async_userdata() -> Result<()> {
                 Delay::new(Duration::from_millis(n)).await;
                 Ok(format!("elapsed:{}ms", n))
             });
+
+            #[cfg(not(feature = "lua51"))]
+            methods.add_async_meta_method(MetaMethod::Call, |_, data, ()| async move {
+                let n = data.0.load(Ordering::Relaxed);
+                Delay::new(Duration::from_millis(n)).await;
+                Ok(format!("elapsed:{}ms", n))
+            });
         }
     }
 
     let lua = Lua::new();
     let globals = lua.globals();
 
-    let userdata = lua.create_userdata(MyUserData(Arc::new(AtomicI64::new(11))))?;
+    let userdata = lua.create_userdata(MyUserData(Arc::new(AtomicU64::new(11))))?;
     globals.set("userdata", userdata.clone())?;
 
     lua.load(
@@ -315,6 +323,16 @@ async fn test_async_userdata() -> Result<()> {
     .exec_async()
     .await?;
 
+    #[cfg(not(feature = "lua51"))]
+    lua.load(
+        r#"
+        userdata:set_value(15)
+        assert(userdata() == "elapsed:15ms")
+    "#,
+    )
+    .exec_async()
+    .await?;
+
     Ok(())
 }
 
diff --git a/tests/conversion.rs b/tests/conversion.rs
index 01880d8..6d17d0a 100644
--- a/tests/conversion.rs
+++ b/tests/conversion.rs
@@ -3,7 +3,7 @@ use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
 use std::ffi::{CStr, CString};
 
 use maplit::{btreemap, btreeset, hashmap, hashset};
-use mlua::{Lua, Result};
+use mlua::{Error, Lua, Result};
 
 #[test]
 fn test_conv_vec() -> Result<()> {
@@ -123,3 +123,18 @@ fn test_conv_boxed_slice() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_conv_array() -> Result<()> {
+    let lua = Lua::new();
+
+    let v = [1, 2, 3];
+    lua.globals().set("v", v)?;
+    let v2: [i32; 3] = lua.globals().get("v")?;
+    assert_eq!(v, v2);
+
+    let v2 = lua.globals().get::<_, [i32; 4]>("v");
+    assert!(matches!(v2, Err(Error::FromLuaConversionError { .. })));
+
+    Ok(())
+}
diff --git a/tests/table.rs b/tests/table.rs
index 6378e5c..b22696d 100644
--- a/tests/table.rs
+++ b/tests/table.rs
@@ -139,14 +139,6 @@ fn test_table_sequence_from() -> Result<()> {
         vec![1, 2, 3]
     );
 
-    assert_eq!(
-        get_table
-            .call::<_, Table>(&[1, 2, 3])?
-            .sequence_values()
-            .collect::<Result<Vec<i64>>>()?,
-        vec![1, 2, 3]
-    );
-
     Ok(())
 }
 
diff --git a/tests/tests.rs b/tests/tests.rs
index 9b450ae..4d76adb 100644
--- a/tests/tests.rs
+++ b/tests/tests.rs
@@ -847,6 +847,37 @@ fn test_mismatched_registry_key() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_application_data() -> Result<()> {
+    let lua = Lua::new();
+
+    lua.set_app_data("test1");
+    lua.set_app_data(vec!["test2"]);
+
+    let f = lua.create_function(|lua, ()| {
+        {
+            let data1 = lua.app_data_ref::<&str>().unwrap();
+            assert_eq!(*data1, "test1");
+        }
+        let mut data2 = lua.app_data_mut::<Vec<&str>>().unwrap();
+        assert_eq!(*data2, vec!["test2"]);
+        data2.push("test3");
+        Ok(())
+    })?;
+    f.call(())?;
+
+    assert_eq!(*lua.app_data_ref::<&str>().unwrap(), "test1");
+    assert_eq!(
+        *lua.app_data_ref::<Vec<&str>>().unwrap(),
+        vec!["test2", "test3"]
+    );
+
+    lua.remove_app_data::<Vec<&str>>();
+    assert!(matches!(lua.app_data_ref::<Vec<&str>>(), None));
+
+    Ok(())
+}
+
 #[test]
 fn test_recursion() -> Result<()> {
     let lua = Lua::new();
@@ -1046,17 +1077,22 @@ fn test_context_thread() -> Result<()> {
         )
         .into_function()?;
 
-    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+    #[cfg(any(
+        feature = "lua54",
+        feature = "lua53",
+        feature = "lua52",
+        feature = "luajit52"
+    ))]
     f.call::<_, ()>(lua.current_thread())?;
 
-    #[cfg(any(feature = "lua51", feature = "luajit"))]
+    #[cfg(any(feature = "lua51", all(feature = "luajit", not(feature = "luajit52"))))]
     f.call::<_, ()>(Nil)?;
 
     Ok(())
 }
 
 #[test]
-#[cfg(any(feature = "lua51", feature = "luajit"))]
+#[cfg(any(feature = "lua51", all(feature = "luajit", not(feature = "luajit52"))))]
 fn test_context_thread_51() -> Result<()> {
     let lua = Lua::new();
 
diff --git a/tests/userdata.rs b/tests/userdata.rs
index 65a3fb2..958da92 100644
--- a/tests/userdata.rs
+++ b/tests/userdata.rs
@@ -111,7 +111,12 @@ fn test_metamethods() -> Result<()> {
                     Err("no such custom index".to_lua_err())
                 }
             });
-            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+            #[cfg(any(
+                feature = "lua54",
+                feature = "lua53",
+                feature = "lua52",
+                feature = "luajit52"
+            ))]
             methods.add_meta_method(MetaMethod::Pairs, |lua, data, ()| {
                 use std::iter::FromIterator;
                 let stateless_iter = lua.create_function(|_, (data, i): (MyUserData, i64)| {
@@ -136,11 +141,16 @@ fn test_metamethods() -> Result<()> {
         10
     );
 
-    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-    let pairs_it = {
-        lua.load(
+    #[cfg(any(
+        feature = "lua54",
+        feature = "lua53",
+        feature = "lua52",
+        feature = "luajit52"
+    ))]
+    let pairs_it = lua
+        .load(
             r#"
-            function pairs_it()
+            function()
                 local r = 0
                 for i, v in pairs(userdata1) do
                     r = r + v
@@ -149,17 +159,21 @@ fn test_metamethods() -> Result<()> {
             end
         "#,
         )
-        .exec()?;
-        globals.get::<_, Function>("pairs_it")?
-    };
+        .eval::<Function>()?;
 
     assert_eq!(lua.load("userdata1 - userdata2").eval::<MyUserData>()?.0, 4);
     assert_eq!(lua.load("userdata1:get()").eval::<i64>()?, 7);
     assert_eq!(lua.load("userdata2.inner").eval::<i64>()?, 3);
-    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
-    assert_eq!(pairs_it.call::<_, i64>(())?, 28);
     assert!(lua.load("userdata2.nonexist_field").eval::<()>().is_err());
 
+    #[cfg(any(
+        feature = "lua54",
+        feature = "lua53",
+        feature = "lua52",
+        feature = "luajit52"
+    ))]
+    assert_eq!(pairs_it.call::<_, i64>(())?, 28);
+
     let userdata2: Value = globals.get("userdata2")?;
     let userdata3: Value = globals.get("userdata3")?;