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On 2019-08-07 8:53 p.m., Egor Skriptunoff wrote:

On Fri, Aug 2, 2019 at 12:14 AM Soni "They/Them" L. wrote:

    Inventory may not be self-contained. Inventory could reference
    another
    trait.



AFAIU "trait" in Rust is the same as "interface" in other languages.
You must implement interface for a class to be able to use it with objects of this class. 
In other words, a trait have to be "rooted" into a class.
That's why I don't understand what do you mean in "Inventory may not be self-contained". Please give a non-trivial example about "a trait could reference another trait" (in Cratera, not in Rust).
My intention was to understand whether the Cratera-like syntax "a:b.c(x)" would bring additional expressiveness to Lua or not (I hope it would, and I guess you can show an example). But there are 10 replies posted already in this thread, and I still can't imagine a real-life use case where traits could lead to a better code (more readable/compact/etc). Is traits really just a Rust-nostalgic feature (as you've said: "It's just a different way of doing OOP"), which actually doesn't add new power to Lua? 



Lua has many ways of doing OOP, Cratera adds a new one on top.
With traits, one can do a "type-system ECS", that gets compiled to extremely efficient runtime code. However, it requires recompiling and doesn't exist (at all) at runtime, which is a bit different from what an ECS would do.
Cratera is my attempt to bring that "type-system ECS" to the runtime. The basic idea is that many of the patterns you'd use in Rust you should also be able to use in Cratera.
You can also, ofc, inject your own traits into existing objects. You can't do that with "OOP". But you can with Cratera. Which means it's not strictly OOP.
(Rust *also* has support for "inject your own traits", sort of. It's a bit limited, as you can't inject not-your-own-crate's traits into not-your-own-crate's types, but it does exist. Sometimes you have to wrap an object in another due to those limitations, which is something you don't in Cratera. This limitation mainly has to do with traits being a type property in Rust, whereas in Cratera they're more of an object property.)
ECS is all about composition, and so are traits. This may be the only similarity between them, but I'm more inclined to believe there are others.