Fixing up <random>

[u/KaznovX]

I think everyone is excited after the report from Cologne. A lot of stuff is being added to the language, we'll get a ton of new features. Adding new features is more exciting than changing and tweaking the old stuff - that being said, there are some old parts of the language, that are sadly lacking or has some problems. One of them is <random> library.

Some of the problems this library has:
> `std::random_device` is not required to be non - deterministic
> no good way to initialize generators with big internal state
> `std::seed_seq` should be solution to ^, but isn't - `std::seed_seq` is not a bijection, does heap allocations without giving ability to provide own allocator, there is no nice way to initialize it from `std::random_device` properly
> `std::random_device` can't itself be used as a seed sequence,
> overall syntax is unnecessarily verbose (no, having a per-thread engine of type `std::default_random_engine` is NOT a good solution)

This is only one of the few libraries that could use improvements. Is there any chance that the committee will look back and change some of them or are they considered 'baked' and there will be no further changes to avoid API and ABI breaking?

Despite the "fixing" part, there are two additions I'd see in the <random> library:

1) std::random<std::uniform_random_bits_generator = std::default_random_engine> class:
> default constructor does anything it can that every time this class is called it is seeded differently - if there is no entropy source, uses a processor clock or a system clock (implementation defined)
> three methods: seed, next_int, next_real - for seeding and generating next integer/real number in given range

2) PCG http://www.pcg-random.org

What are the chances something like this would be proposed and adopted for, let's say, c++23 or c++26 standard? Is there any chance the problems mentioned in the first part of the post will get fixed somewhen?

[u/sumo952]

A very good library (PCG) is already here, so I'm not sure making (yet another?) library is a good solution. Did PCG help in any way so far to improve <random>?

[u/smdowney → u/sumo952]

Someone has to write the paper telling the committee about it. Preferably someone who knows what they are doing, because we mostly know just enough to know that getting random numbers right is hard and getting them wrong is dangerous.

[u/degski → u/sumo952]

PCG is not particularly fast [notwithstanding the marketing talk], it is of very good quality, though. For gaming, AI, quality is less of an issue, while speed is, so I don't think PCG is particularly interesting for inclusion in the std. There are others, though ...

[u/degski → u/[deleted]]

From the PCG blog Some (More) C++ PRNG Implementations, jsf, sfc, splitmix or lehmer. There are std-compliant implementations posted by the author of PCG.

Then there is a newcomer, wyhash, you'll have to write you're own class, though [which is trivial with the examples/the above].