Executor integration with filters

[shrijitsingh99]

This will serve as a base PR for all executor integration related aspects.

TODO:

Update: This will be the first PR to be merged into PCL, after this all the remaining PR's are to be merged.

[kunaltyagi]

Anything to review here or has the code arrived here after review?

[SergioRAgostinho]

It's 1000 loc 😱

[SergioRAgostinho]

Feedback from quickly skimming at the code. Move all those C++17 traits you added to the common module. I'm sure they'll be useful in other locations of the library.

[shrijitsingh99]

Uh oh! Sorry didn't realize this became a huge PR. Will split this into 2 PRs. Most of the LOC are directly from the files from the executor repo.

[kunaltyagi]

Sorry, but could you split this in 1 of 2 ways:

• 2 commits: 1 for the changes to Filter and FilterIndices and the other for everything else
• 2 PRs: same split as in prev point

[shrijitsingh99]

2 commits: 1 for the changes to Filter and FilterIndices and the other for everything else

Done

Move all those C++17 traits you added to the common module

Will do that once best_fit is ready, during the final porting

[kunaltyagi]

2 things for commit 1:

• Filter calls without executor should route to filter with best-fit executor: Please note as TODO somewhere
• PCLPointCLoud2 is not supported yet: either an oversight or needs to be documented well

[kunaltyagi]

LGTM (apart from comments)

Please allow for a migration path too. We might need to have a discussion on this but for starters, I see 2 ways:

• Copy + rename old code
• Have 3 classes:
  1. EaseOfImpl: common code, hidden in detail namespace
  2. Legacy: no CRTP, new name, derived from EaseOfImpl
  3. New hierarchy: old name, derived from EaseOfImpl

Eg:

FilterImpl {};

// maybe we wouldn't mark this as deprecated since this might be a very simple class
// Plus it also prevents us from using -Werror on the CI
FilterLegacy: FilterImpl{};

template <class Derived>
Filter: FilterImpl{
  void new_function() {
    static_cast<Derived*>(this)->virtual_function();
  }
};

template <class BaseClass>
ABCFilterImpl: BaseClass {};

// mark as deprecated
ABCFilterLegacy: ABCFilter<FilterLegacy>{
  // code specific to making legacy work
};

ABCFilter: ABCFilter<Filter>{};

[kunaltyagi]

No migration path needed. LGTM except:

• no code in executor-less call to filter
• warning
• better documentation (1 line brief doesn't count)

[shrijitsingh99]

Any more changes needed or we are good to go?