[Pre-RFC] named arguments

[djc]

@DanielKeep

It shouldn't be that difficult to understand.

Every single new feature has tremendous long-term costs. It has to implemented, then maintained at least until the next breaking version (which might be years away, if ever). It has to be documented. It has to be explained. It has to be considered when designing and writing code, yet another moving part to keep in mind. It's yet another piece of syntax for new users to see and think "what the heck is that?" and then have to try and google syntax (which never works well). It's hundreds of the same Stack Overflow questions over and over again because so many people don't bother to search, or don't know what they're searching for in the first place, or how to word it.

I understand all that. By saying I'm baffled I'm signalling that I have a very different perception of cost/benefit of this feature compared to Nick/Graydon (in particular). Also please note that, by saying I'm baffled I'm saying that I don't understand, which is very different from "rejecting your opponents as insane". Obviously noone here is insane, I just disagree vehemently on the perception some people seem to have of this feature.

A grammar construct that doesn't get used for something else seems like a good thing, that's focus. We have to work out how it interacts with the type system, but I haven't heard great arguments why it cannot. Also, I haven't seen many edge case minutiae where it actually goes wrong.

Saying you don't need this, to me, is limiting yourself to a narrow level of what code is. If you look at code as an ecosystem, at evolving libraries, at people learning new APIs and extending the surface of an API that they're familiar with, then I think you do need this. It may not be essential-essential, but I believe it's very important.

I'm not saying Rust should "grab every feature"; this particular one, combined with optional arguments (see also my pre-RFC), seems to be one of the most popular requests. That, by itself, should give everyone some food for thought. Yes, sometimes the customer doesn't know what he/she needs, but I haven't heard any alternative from the opposition that seems credible (I certainly don't think anonymous structs are a viable alternative).