[iamed2]

This is truly an important issue. Right now, every interface represents something that needs to be documented by the author. The AbstractArray and Iteration interfaces are well-documented, but the AbstractDict interface isn't. I believe that documentation for an interface is enough, but I also don't think enough people will take the time to write it. So I agree there should be a technical solution.

The main reason this has not been implemented as a language feature is that people are worried about settling on a design that would be impossible to make fast and concise. It is certainly on the designers' radar, and was discussed specifically at JuliaCon 2017 in Jeff Bezanson's talk.

There are some people who plan to attempt a trait system as a package on Julia 1.0. Perhaps this will be successful and we won't need language changes! Stay tuned.

As an aside, I wouldn't take the lack of action as lack of interest. People are interested, but it wasn't prioritized yet. It will get effort and attention!

[dnbgfher]

I think you need language changes no matter what. I've seen some of the previous trait packages and while extremely cool, they're insufficent for tackling this problem for a couple reasons.

First, this extends deep into the core of Julia, and I don't see how a traits package would be involved with that.

Second, and this dovetails with the first issue, this needs to be something that people actually use as a default action. Part of that means ensuring the built-in types make use of this.

Related to all of this, I worry it's too late to really make a meaningful change here. The culture and existing packages are already set without it. Adding the feature as a requirement isn't going to happen anytime soon unless people are willing to continue to break things post 1.0. And it needs to be a requirement or it won't get used except by people that will already provide documentation.

The lack of interest I mentioned mainly came from some github issues which either received little attention, had creators that had a very "maybe it would be nice if" attitude, and responses that were questioning the benefit compared to the cost of implementing the syntax changes.

[ChrisRackauckas]

>First, this extends deep into the core of Julia, and I don't see how a traits package would be involved with that.

No, Tim Holy described over dinner how all that was necessary to complete the existing traits packages was method deletion, and that's in v1.0.

[dnbgfher]

Interesting.

But as an external package it still has the issues I described as not being part of the defaults of the culture. Without that it just becomes a nice-to-have that only people serious about writing good quality, usable code are going to use. And these are the people most likely to have good documentation in any case.

[ChrisRackauckas]

Yes indeed, but the cultural issue can be addressed by adding it into Base in a 1.x since it's not breaking. I don't think it will make it into a 1.x though but it can.