Re: Lua 5.4 Tuples FTW!

[Thomas Jericke <tjericke@...>]

On 16.03.2018 11:11, Duane Leslie wrote:

On 16 Mar 2018, at 17:54, Thomas Jericke <tjericke@indel.ch> wrote:

The problem I see, is that you don't get raw equality with any userdata implementation of tuples. So I cannot use them as table keys.

This can be solved using interning as is often done with strings, it just makes the constructor function more difficult and requires a `__gc` metamethod.

Just.

Well I see how this can work, but then, this is nothing that could not be done with Lua 5.3 and tables.

Also they are passed by reference and not by value. That can be confusing once you edit a value in that tuple.

The passing method doesn't matter if the tuple is immutable (or copy-on-edit) so this isn't an issue.

Regards,

Duane.

I am actually struggling a little how I would implement a copy-on-edit. The __newindex metamethod gets the userdata and the field name and the new value as parameters. The userdata is passed as a reference, but if I am not completely wrong I cannot edit the original reference, I just get a copy of the reference which is then placed on the stack. If Lua wanted to support this, it would need to be possible that the __newindex method returns a value that replaces the original reference.I haven't tried this so I might be wrong here.

Anyway the resort to immutable will work for sure.
--
Thomas