Question: Is MetaMethod::IPairs missing for lua54? #635

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1. khvzak commented on Aug 31, 2025

   

   khvzak

   on Aug 31, 2025

   Last edited by khvzak

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   Lua 5.4 does not support __ipairs metamethods (it was removed since 5.3).

   You can use __index instead:

   struct MyUserData(i32);
   
   impl LuaUserData for MyUserData {
       fn add_methods<M: LuaUserDataMethods<Self>>(methods: &mut M) {
           methods.add_meta_method(LuaMetaMethod::Index, |_lua, this, k: i32| {
               if k < this.0 {
                   return Ok(Some(k * k));
               }
               Ok(None)
           });
       }
   }
   
   lua.load(
       r#"
       my_ud = ...
       for i, x in ipairs(my_ud) do
           print(i, x)
       end
   "#,
   )
   .call::<()>(MyUserData(5))
   .unwrap();

   or simply provide your own iterator function.

   If you want to remove ipairs support, then your __index should return a error for integer keys.
2. mlua-rs

   locked and limited conversation to collaborators on Aug 31, 2025
3. khvzak

   converted this issue into a discussion #636 on Aug 31, 2025