Feature: generic matchers

[melak47]

Description

Currently, composable matchers are based on MatcherBase<T>, like EqualsMatcher<T>.
EqualsMatcher<T> can compare two std::vector<T>s for equality, but not a std::vector and a std::array, for example.
This can make writing tests cumbersome somtimes, as you either need to write your own matcher
for whatever containers you need to work with, or convert everything to std::vector.

This PR aims to implement support for matchers that can be generic in their argument types, while also:

• not breaking compatibility with existing matchers
• allowing combining generic and non-generic matchers via &&, ||, !
• (ideally) not impacting compile time of code that only uses non-generic matchers

Here is a motivating example:

TEST_CASE("example") {
    std::array<int, 3> container{1,2,3};

    std::array<int, 3> a{1,2,3};
    std::vector<int> b{0,1,2};
    std::list<int> c{4,5,6};

    CHECK_THAT(container, EqualsRange(a) || EqualsRange(b) || EqualsRange(c));
}

While it's easy to write your own custom EqualsRange matcher, making it composable with other matchers using &&, ||, ! is not, since that requires deriving from a shared MatcherBase<T>.

With the changes from this PR, an implementation of EqualsRange could look like this:

template<typename Range>
struct EqualsRangeMatcher : Catch::MatcherGenericBase {

    EqualsRangeMatcher(Range const& range) : range{range} {}

    template<typename OtherRange>
    bool match(OtherRange const& other) const {
        using std::begin;
        using std::end;

        return std::equal(begin(range), end(range), begin(other), end(other));
    }

    std::string describe() const override {
        return "Equals: " + Catch::rangeToString(range);
    }

private:
    Range const& range;
};

template<typename Range>
auto EqualsRange(const Range& range) -> EqualsRangeMatcher<Range> {
    return EqualsRangeMatcher<Range>{range};
}

[codecov]

Codecov Report

Merging #1843 into dev-v3 will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           dev-v3    #1843      +/-   ##
==========================================
+ Coverage   89.12%   89.24%   +0.12%     
==========================================
  Files         142      144       +2     
  Lines        6037     6133      +96     
==========================================
+ Hits         5380     5473      +93     
- Misses        657      660       +3     

[horenmar]

I fixed it up a bit.

[horenmar]

How about operator,? 😈

[melak47]

I don't think anything here is vulnerable to that right now, but it can't hurt :)

[horenmar]

I would add ! just to be thorough.

[horenmar]

Cool, thanks.

[horenmar]

This include should not be needed (I am also not sure what is used for, but I did not look hard)

[melak47]

I forgot to remove the include.

[melak47]

Sorry, rebased again.