Create a helper Proxy struct for retriving proxied types as function arguments

src/table.rs

@@ -1,4 +1,3 @@
-
 use mlua_sys as lua;
 
 use crate::{ensure_type, AsLua, FromLua, FromLuaStack, LuaRef, PushToLuaStack, Result, StackGuard, State, Value};
@@ -324,14 +323,67 @@ impl<'a> AsLua<'a> for Table<'a> {
 /// with minimizing the amount of calls to and from Rust.
 pub trait TableProxy: Sized {
     /// Create an instance of `Self` from the table
-    fn from_table<'a>(state: &'a State, table: Table<'a>) -> Result<Self>;
+    fn from_table<'a>(lua: &'a State, table: Table<'a>) -> Result<Self>;
     /// Creates a Lua instance from `Self`
     fn as_table<'a>(&self, state: &'a State) -> Result<Table<'a>>;
 }
 
+/// A struct that wraps a Proxied value. It can be used to get 
+pub struct Proxy<T: TableProxy> {
+    data: Option<T>,
+}
+
+impl<T: TableProxy> Proxy<T> {
+    pub fn new() -> Self {
+        Self {
+            data: None,
+        }
+    }
+
+    /// Retrieves the data from the proxy, if there is no data, it will panic.
+    pub fn take(self) -> T {
+        self.data
+            .expect("the proxy was not provided any data")
+    }
+
+    /// Retrieves the data from the proxy, returns `None` if the Proxy has no data.
+    pub fn try_take(self) -> Option<T> {
+        self.data
+    }
+}
+
+impl<T: TableProxy> From<T> for Proxy<T> {
+    fn from(value: T) -> Self {
+        Self {
+            data: Some(value),
+        }
+    }
+}
+
+// should proxying from lua be implicit by implementing this trait for T, instead of Proxy?
+// it would make it easier, but its more difficult to tell if code is proxying from lua, or
+// getting a borrow.
+impl<'a, T: TableProxy> FromLua<'a> for Proxy<T> {
+    fn from_lua(lua: &'a State, val: Value<'a>) -> crate::Result<Self> {
+        let table = val.into_table()?;
+        let t = T::from_table(lua, table)?;
+
+        Ok(Self::from(t))
+    }
+}
+
+impl<'a, T: TableProxy> AsLua<'a> for Proxy<T> {
+    fn as_lua(&self, lua: &'a State) -> crate::Result<Value<'a>> {
+        self.data.as_ref()
+            .ok_or(crate::Error::Nil)
+            .and_then(|d| d.as_table(lua))
+            .map(|t| Value::Table(t))
+    }
+}
+
 #[cfg(test)]
 mod tests {
-    use crate::{tests::Vec2, Function, State, StdLibrary, Table, TableProxy};
+    use crate::{tests::Vec2, Function, Proxy, State, StdLibrary, Table, TableProxy};
 
     impl TableProxy for Vec2 {
         fn from_table<'a>(_state: &'a crate::State, table: crate::Table<'a>) -> crate::Result<Self> {
@@ -461,4 +513,71 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn table_proxy_value() -> crate::Result<()> {
+        let lua = State::new();
+        lua.expose_libraries(&[StdLibrary::Debug, StdLibrary::Package]);
+    
+        let globals = lua.globals()?;
+        let add_fn = lua.create_function(|_, (a, b): (Proxy<Vec2>, Proxy<Vec2>)| {
+            let a = a.take();
+            let b = b.take();
+
+            let x = a.x + b.x;
+            let y = a.y + b.y;
+            
+            Ok(Proxy::from(
+                Vec2 {
+                    x,
+                    y
+                }
+            ))
+        })?;
+        globals.set("add_vec2", add_fn)?;
+
+        let res = lua.load(
+            "test.lua",
+            r#"
+                require("util")
+
+                Vec2 = { x = 0.0, y = 0.0 }
+                Vec2.__index = Vec2
+                Vec2.__name = "Vec2"
+                
+                function Vec2:new(x, y)
+                    local v = {}
+                    setmetatable(v, Vec2)
+                    
+                    v.x = x
+                    v.y = y
+                    
+                    return v
+                end
+
+                function Vec2:__tostring()
+                    return "Vec2(" .. self.x .. ", " .. self.y .. ")"
+                end
+
+                function do_math()
+                    return Vec2:new(15, 20)
+                end
+
+                local v1 = Vec2:new(15, 20)
+                local v2 = Vec2:new(7, 10)
+                local v3 = add_vec2(v1, v2)
+
+                assert(v3.x == 22 and v3.y == 30, "The result from adding the values was incorrect!")
+                
+                --print("v3 is " .. dump_table(v3))
+                --print("Added together, v3 is " .. tostring(v3))
+        "#)?.execute::<_, ()>(());
+
+        // pretty print the error
+        if let Err(err) = res {
+            panic!("{}", err);
+        }
+
+        Ok(())
+    }
 }