class RSpec::Matchers::BuiltIn::ContainExactly::PairingsMaximizer

Once we started supporting composing matchers, the algorithm for this matcher got much more complicated. Consider this expression:

expect(["fool", "food"]).to contain_exactly(/foo/, /fool/)

This should pass (because we can pair /fool/ with “fool” and /foo/ with “food”), but the original algorithm used by this matcher would pair the first elements it could (/foo/ with “fool”), which would leave /fool/ and “food” unmatched. When we have an expected element which is a matcher that matches a superset of actual items compared to another expected element matcher, we need to consider every possible pairing.

This class is designed to maximize the number of actual/expected pairings – or, conversely, to minimize the number of unpaired items. It’s essentially a brute force solution, but with a few heuristics applied to reduce the size of the problem space:

* Any items which match none of the items in the other list are immediately
  placed into the `unmatched_expected_indexes` or `unmatched_actual_indexes` array.
  The extra items and missing items in the matcher failure message are derived
  from these arrays.
* Any items which reciprocally match only each other are paired up and not
  considered further.

What’s left is only the items which match multiple items from the other list (or vice versa). From here, it performs a brute-force depth-first search, looking for a solution which pairs all elements in both lists, or, barring that, that produces the fewest unmatched items.

@private

Constants

NullSolution

@private Starting solution that is worse than any other real solution.

Solution

@private

Attributes

actual_to_expected_matched_indexes[R]
expected_to_actual_matched_indexes[R]
solution[R]

Public Class Methods

new(expected_to_actual_matched_indexes, actual_to_expected_matched_indexes) click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 225
def initialize(expected_to_actual_matched_indexes, actual_to_expected_matched_indexes)
  @expected_to_actual_matched_indexes = expected_to_actual_matched_indexes
  @actual_to_expected_matched_indexes = actual_to_expected_matched_indexes

  unmatched_expected_indexes, indeterminate_expected_indexes =
    categorize_indexes(expected_to_actual_matched_indexes, actual_to_expected_matched_indexes)

  unmatched_actual_indexes, indeterminate_actual_indexes =
    categorize_indexes(actual_to_expected_matched_indexes, expected_to_actual_matched_indexes)

  @solution = Solution.new(unmatched_expected_indexes,     unmatched_actual_indexes,
                           indeterminate_expected_indexes, indeterminate_actual_indexes)
end

Public Instance Methods

find_best_solution() click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 239
def find_best_solution
  return solution if solution.candidate?
  best_solution_so_far = NullSolution

  expected_index = solution.indeterminate_expected_indexes.first
  actuals = expected_to_actual_matched_indexes[expected_index]

  actuals.each do |actual_index|
    solution = best_solution_for_pairing(expected_index, actual_index)
    return solution if solution.ideal?
    best_solution_so_far = solution if best_solution_so_far.worse_than?(solution)
  end

  best_solution_so_far
end

Private Instance Methods

apply_pairing_to(indeterminates, original_matches, other_list_index) click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 301
def apply_pairing_to(indeterminates, original_matches, other_list_index)
  indeterminates.inject({}) do |accum, index|
    accum[index] = original_matches[index] - [other_list_index]
    accum
  end
end
best_solution_for_pairing(expected_index, actual_index) click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 285
def best_solution_for_pairing(expected_index, actual_index)
  modified_expecteds = apply_pairing_to(
    solution.indeterminate_expected_indexes,
    expected_to_actual_matched_indexes, actual_index)

  modified_expecteds.delete(expected_index)

  modified_actuals = apply_pairing_to(
    solution.indeterminate_actual_indexes,
    actual_to_expected_matched_indexes, expected_index)

  modified_actuals.delete(actual_index)

  solution + self.class.new(modified_expecteds, modified_actuals).find_best_solution
end
categorize_indexes(indexes_to_categorize, other_indexes) click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 265
def categorize_indexes(indexes_to_categorize, other_indexes)
  unmatched     = []
  indeterminate = []

  indexes_to_categorize.each_pair do |index, matches|
    if matches.empty?
      unmatched << index
    elsif !reciprocal_single_match?(matches, index, other_indexes)
      indeterminate << index
    end
  end

  return unmatched, indeterminate
end
reciprocal_single_match?(matches, index, other_list) click to toggle source
# File lib/rspec/matchers/built_in/contain_exactly.rb, line 280
def reciprocal_single_match?(matches, index, other_list)
  return false unless matches.one?
  other_list[matches.first] == [index]
end