dlib::optional

[pfeatherstone]

This is work in progress.
This is inspired by Sy Brand's tl::optional repo and https://github.com/bitwizeshift/BackportCpp.git
I've tried a few different ways of doing things. For example, i didn't like using union but it turns out you can't use aligned_storage if you want things to be constexpr and direct initialization to work.
I have to say, this is an education in C++ initialization. It's laughable how complicated an object that is either active or None can be. C++ is so messed up. And yet, I love it

[pfeatherstone]

It's ready. I think it's a good addition

[davisking]

Sweet, I'll look in a bit :D

[pfeatherstone]

@davisking Have you had a chance to look at this ?

[davisking]

Sorry, not yet. Haven't forgotten though 😅

[pfeatherstone]

I quite like the .then() pattern, i.e. continuations. I wonder how hard it would be to enhance dlib::thread_pool to support continuations on tasks and combine them using free functions like when_all(), when_one(), when_seq(), or alternatively using &&, ||, >>. Then use another function wait() to wait for the task graph to complete.

[davisking]

I quite like the .then() pattern, i.e. continuations. I wonder how hard it would be to enhance dlib::thread_pool to support continuations on tasks and combine them using free functions like when_all(), when_one(), when_seq(), or alternatively using &&, ||, >>. Then use another function wait() to wait for the task graph to complete.

Yeah, depends on how heavy handed you want the implementation to be. Like if every call to any of these functions spawned a new thread that just waited on the future(s) to be ready that's easy. But something less heavyweight gets tricky fast.

[davisking]

This is real nice. I just spent nearly 2 hours reading it all over and trying to find problems but couldn't find any. Thought I saw a bug at one point but was wrong :)

Thanks for the awesome PR.