[phobos] Decision on length of deprecation cycle

[Jonathan M Davis]

The deprecation cycle has three phases:

1. Scheduled for deprecation
2. Deprecated
3. Removed

We have several items in Phobos which are currently in phase 1 and possibly 
some in phase 2 (though I can't think of any off the top of my head). However, 
as far as I know, no decision has been made as to how long something is 
typically in phases 1 or 2 before it actually goes to phase 3 and is removed. 
I know that it's been brought up a couple of times, but I'm not aware of a 
decision being made. As we do have stuff which is in the deprecation cycle, I 
think that we need to have at least a rough idea as to how long we intend the 
average item to be in phases 1 and 2. As such, we need to make a decision. How 
long will each phase be? 6 months each? Longer? Shorter?

I would think that items which are very new but still end up being put in the 
deprecation cycle don't have to take as long, and perhaps items which have 
been around for a long time (such as stuff which is in Phobos 1) should take 
longer than average. But we need to at least decide on what we want the 
typical length of time to be.

For simplicity, 6 months for each phase each sounds good to me, but it would 
be nice for some stuff if it were shorter, since sometimes the old stuff has 
to be actually removed in order for new functionality to take its place (e.g. 
std.array has some of its functions being renamed to have InPlace in their 
names, since they operate in place, but versions which do not operate in place 
cannot replace them until the old versions have been completely removed). So, 
6 months for each phase could be a bit long (since then it would be a year 
before something actually was removed from Phobos once it entered the 
deprecation cycle). I really don't know what others might consider reasonable 
though.

Regardless, I think that we need to make an actual decision on how long stuff 
will typically be in each phase of deprecation, even if some stuff ends up 
being removed faster or sticking around longer, depending on its particular 
circumstances.

- Jonathan M Davis