Re: Interest in a Unicode library for Boost?

From: Gavin Lambert (boost_at_[hidden])
Date: 2019-11-03 22:24:07

On 2/11/2019 04:34, Zach Laine wrote:
> This is a red herring; if you only care about existence, why are you 
> using find()?  Use any_of() or C++20's includes() (for detecting 
> subranges) instead.  They each return a bool.  Moreover, just knowing 
> whether a value is found at all within a subrange via linear search is a 
> corner case -- usually you will use something with O(log(N)) or faster 
> access if you need to do that operation a lot.

I'm using find because you said to use find. :)

But yes, the argument applies to map.find and friends as well -- and 
would probably be more useful there than for std::find itself.  "Is key 
present in map" is a very common query.

(Granted, map.contains has been added in C++20, but most people don't 
have access to that yet.)

> If I had to write that code using your approach, it would suffer.  All 
> I'm pointing out here is that the change you propose is not universally 
> better.  In fact, it is universally worse if what you want to do is 
> search for a subrange:
> 
> auto lower =Â std::lower_bound(c.begin(), c.end(), 42);
> out = std::copy(lower, std::upper_bound(lower, c.end(), 42), out);
> 
> Or:
> 
> out = std::ranges::copy(std::ranges::equal_range(c, 42), out);
> 
> That turns in to a real mess when the iterators returned are optionals.

I don't really like the former example anyway because you're not 
checking for failure of lower_bound.  Granted, it will end up with an 
empty range in the end so the result will still be correct, but you're 
potentially wasting some time in upper_bound.

In the second example it would return an empty range either way, so 
there's not really any difference.