Added sync2.Set

[Alexamakans]

Thread-safe set.

[Alexamakans]

Would rather see the implementation make use of sync2.Map instead, as it already contains all the complex logic for having a lock-free map.

Do those complexities apply when it's used as a set? Is it mainly complex because of the dirty/readonly portion of it?

Haven't looked at it a whole lot nor thought about the issue, will check it out.

I've strictly been staying away from dependencies for this repo, even in testing, because I want this repo to be a dependency-free implementation where it's completely standalone. It's a silly constraint, but I want to stick with it.

I imagined this was the case when I saw there were none, I see now that it's written in the README.md as well. I like this constraint 👍🏻

Will look at doing it without dependencies.

• Mix of responsibility for the sync2 package, especially considering the copied Product type and CartesianProduct function. The code better belongs inside the sets package, and given the added set type then maybe sets.Set should be an interface? Just a thought.
• There's no good interop with sets.Set. There's a wrap method, but that's pretty clunky.

Both good points. In addition to maybe using sync2.Map instead, I will also likely look at alternative ways to make it fit better in pkg/sets.

[applejag]

Ok I got a plan:

• move sets.Set to maps.Set, as it's a set implementation based on the map

• keep this as sync2.Set, as it does live nicely next to sync2.Map

• change it to use sync2.Map for the implementation.

• do a major version bump.

• make CartesianProduct function work on interfaces instead so it can be used on both sync2.Set and maps.Set.

• probably rename some methods along the way, as I at least still always confuse SetDiff with SymDiff.

Do you want to give this a shot, or shall I apply my proposed changes?

[Alexamakans]

Sounds good. I'll give it a shot 👍🏻

Copy-pasting for checklist:

• [x] move sets.Set to maps.Set, as it's a set implementation based on the map
• [x] keep this as sync2.Set, as it does live nicely next to sync2.Map
• [x] change it to use sync2.Map for the implementation.
• [x] do a major version bump.
• [x] make CartesianProduct function work on interfaces instead so it can be used on both sync2.Set and maps.Set.
  • Currently returns a built-in map, map[Product[TA, TB]]struct{}.

I think the method names are good, SetDiff and SymDiff feel more like "gotta get used to it" or "find something that makes it click for you" rather than bad names hehe 😜 - [ ] probably rename some methods along the way, as I at least still always confuse SetDiff with SymDiff.

[applejag]

Regarding the REUSE compliance, I suggest:

• Files you've created completed from scratch, add your own copyright, e.g:

  // SPDX-FileCopyrightText: 2022 <your name>
  //
  // SPDX-License-Identifier: MIT

• Files you've taken based on my files, add your copyright to the same that was in the forked file, e.g:

  // SPDX-FileCopyrightText: 2022 <your name>
  // SPDX-FileCopyrightText: 2022 Kalle Fagerberg
  //
  // SPDX-License-Identifier: MIT

As I license this under MIT, I require that you're OK with licensing your code under MIT as well

[Alexamakans]

Regarding the REUSE compliance, I suggest:

• Files you've created completed from scratch, add your own copyright, e.g:

  // SPDX-FileCopyrightText: 2022 <your name>
  //
  // SPDX-License-Identifier: MIT

• Files you've taken based on my files, add your copyright to the same that was in the forked file, e.g:

  // SPDX-FileCopyrightText: 2022 <your name>
  // SPDX-FileCopyrightText: 2022 Kalle Fagerberg
  //
  // SPDX-License-Identifier: MIT

As I license this under MIT, I require that you're OK with licensing your code under MIT as well

Not sure I have done this for every applicable file, but I think I got them all.

[Alexamakans]

The duplication it's complaining about is solely the test code for sync2.Set and maps.Set. Make it nicer, or is this acceptable?

[applejag]

The duplication it's complaining about is solely the test code for sync2.Set and maps.Set. Make it nicer, or is this acceptable?

Acceptable.