5.2: equality for closures

[Alexander Gladysh <agladysh@...>]

Hi, list!

I apologize if this was already discussed. If this is the case, please
point me to the right message.

I have a problem with this clause from the Manual, section 3.4.3 —
Relational Operators:

> Closures with the same reference are always equal.
> Closures with any detectable difference (different behavior,
> different definition) are always different.

(I assume that this applies to the case then closure is used as table
key as well.)

In our code we heavily use this function:

local unique_object = function()
    -- Note that table is not acceptable, since its contents are not constant.
    return function() end
end

It returns globally unique constant object that then (usually) is used
as a table key (usually to avoid name clashes).

Note, as comment says, the object can not be table — tables can be
changed, and, with Lua dynamic type system, this *will* lead to weird
bugs, where unique_object() result is accidentally used instead of a
table.

In 5.2 this function will no longer work due to above quote. And I
will not even be able to use newproxy() instead — as I understand
newproxy() is no more.

Please do not suggest to generate a Lua code string and then load it
to get a function — it is not acceptable, way too slow.

I understand that the new equality rules for closures are here as
(probably useful) optimization. But they kill a very useful idiom.

Any suggestions on how to workaround this?

Alexander.