Add version of GetUnits to take a set of filters

[ImpulseCloud]

Is your feature request related to a problem? Please describe.
Currently, only 1 type of Filter can be passed to GetUnits to return a filtered list of units. We then have to do additional manually filtering after the initial call.

Describe the solution you'd like
It would be great to use multiple filters in one call.

alkurbatov: "i.e. assuming that we have IsNonSaturatedTownHall, IsTownHall and IsFinished it would be convenient to use e.g. 'AllOf' predicate which uses inside all of these." -- "I suggest to add it ... in the form of a separate call like getUnits, but getUnitsAllOf with array of filters passed by reference. In this case the implementation will be much simpler."

Describe alternatives you've considered
Instead of an array of filters, allow sequential chaining composition. [e.g. .GetUnits( IsNonSaturated( IsFinished( IsTownHall())) ) ] A filter could take a filter input and output a compound filter.

References for different chaining syntaxes:
https://www.fluentcpp.com/2019/08/06/chaining-output-iterators-into-a-pipeline/
http://cpptruths.blogspot.com/2014/03/fun-with-lambdas-c14-style-part-1.html
https://stackoverflow.com/questions/8367879/c-lambda-expression-for-method-chains
https://chriskohlhepp.wordpress.com/advanced-c-lisp/lambda-over-lambda-in-cplusplus14/

[kubivan]

I'm working on api extensions, and resolved the problem in the following way:
https://github.com/kubivan/sc2-bot/blob/master/src/utils/UnitQuery.h
so, you can easily implement your own filters, even in compile time sometimes:

const auto is_mineral = type(UNIT_TYPEID::NEUTRAL_MINERALFIELD) || type(UNIT_TYPEID::NEUTRAL_MINERALFIELD750);
const auto is_resource = is_mineral || is_gas;
const auto resources_around_probe = obs->GetUnits(is_resource && in_radius(probe_pos, 10 ));

[Nickrader]

I assumed this issue meant we wanted a variable number of arguments to be passable to GetUnits (or similar function).
I started with looking at Variadic templates, but couldn't figure it out. Then more googling pointed me to std::initializer_list.

So I think I have the start of a solution with overloading GetUnits() using a std::initializer_list.
That way the user doesn't have to change the function to use lists.
I have only implemented a rudimentary test in tutorial bot to test it, seems to work.
I assume it is duplicating units in the pool should they fall into multiple filters.
The testing framework still will take me time to learn.

https://github.com/Nickrader/cpp-sc2/blob/iss_98/src/sc2api/sc2_client.cc

Units GetUnits(std::initializer_list<Filter> filters) const final;

Units ObservationImp::GetUnits(std::initializer_list<Filter> filters) const {
    Units units;
    std::initializer_list<Filter>::iterator it = filters.begin();
    for (it; it != filters.end(); ++it ) {
        const Filter arg = *it;
        unit_pool_.ForEachExistingUnit([&](Unit& unit) {
            if (arg(unit)) {
                units.push_back(&unit);
            }
        }
        );
    }
    return units;
}

https://github.com/Nickrader/cpp-sc2/blob/iss_98/include/sc2api/sc2_interfaces.h

    //! Get all units belonging to self that meet the conditions provided by the list of filters. The unit structure is const data only.
    //! Therefore editing that data will not change any in game state. See the ActionInterface for changing Unit state.
    //!< \param filter A functor or lambda used to filter out any unneeded units in the list.
    //!< \return A list of units that meet the conditions provided by the filter.
    virtual Units GetUnits(std::initializer_list<Filter>) const = 0;

Open on thoughts on where to go from here, or refinements to make, or if I am missing something and this isn't the right path.

[Nickrader]

Here is my new and improved attempt.
Nickrader@5129366

It lacks testing at the moment, beyond the simple test I put in Tutorial.cc

also, edited sc2_api.h for convenience, but that can be undone and include statements added in the working file.