Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30

Subject: Re: [boost] [review] The review of Boost.DoubleEnded starts today: September 21 - September 30
From: Thorsten Ottosen (tottosen_at_[hidden])
Date: 2017-09-26 17:30:53

Hi Degski,

Thanks for your time.

> Playing around with devector, I find the default growth strategy (x4) >
> rather (too) agressive. It also has some in my view un-intended effects.
> Starting from let's say initial front and back capacities of each 4, now
> adding 5 elements in front and 5 elements in the back (so 10), now gives me
> a devector with capacity 128 (wow, why bothr with SBO at all).

There is room for improvement here.

https://github.com/facebook/folly/blob/master/folly/docs/FBVector.md

recommends 1.5. But if I used it as a local buffer, a bigger value might 
be warranted (so at least the user can choose).

> Then looking how the free_capacity is split between front and back we get
> 95 and 23 (or the other way around, depending on whether we first push_back
> or first push_front, even when front- and back-pushes are interleaved). As
> we are multiplying by 4, this will become more and more skewed.

Yeah, but would it not become more and more skewed no matter what number 
 >1 we multiply with?

Is there any way to avoid that? Is it desirable to avoid that? The 
analog for vector is that it has (with a growth factor of 2) on average 
25% unused objects. As the container grows, so does the wasted space in 
absolute terms.

> Some bikeshedding (tm). I don't like any of the names much. The batch_deque
> *is* a deque, it should be called that way. devector is a hybrid
> vector/deque, I think veque would capture that. Then as to double_ended, I
> think it's too long and describes badly what we are talking about. I
> haven't got any (much) better proposal, but was thinking of Boost.Que, nice
> and short.
> 
> i.e. boost::que::veque and boost::que::deque.

I think it's great to do some bikeshedding. Keep doing that.

kind regards

Thorsten