This implementation is much more complex, and is optimized for rare (or hopefully no) updates once the queries start. Updates incur a cost as it has to clear the memoization and keep track of applicable keys. Queries will be O(N) the first time an item is provided with a given set of applicable metadata; subsequent queries with items with the same set of applicable metadata will be O(1) due to internal memoization.
This is ideal for use by config, where filterable items (e.g. hooks) are typically added at the start of the process (e.g. in `spec_helper`) and then repeatedly queried as example groups and examples are defined. @private
# File lib/rspec/core/metadata_filter.rb, line 156 def initialize(applies_predicate) super @applicable_keys = Set.new @proc_keys = Set.new @memoized_lookups = Hash.new do |hash, applicable_metadata| hash[applicable_metadata] = find_items_for(applicable_metadata) end end
# File lib/rspec/core/metadata_filter.rb, line 165 def append(item, metadata) super handle_mutation(metadata) end
# File lib/rspec/core/metadata_filter.rb, line 175 def items_for(metadata) # The filtering of `metadata` to `applicable_metadata` is the key thing # that makes the memoization actually useful in practice, since each # example and example group have different metadata (e.g. location and # description). By filtering to the metadata keys our items care about, # we can ignore extra metadata keys that differ for each example/group. # For example, given `config.include DBHelpers, :db`, example groups # can be split into these two sets: those that are tagged with `:db` and those # that are not. For each set, this method for the first group in the set is # still an `O(N)` calculation, but all subsequent groups in the set will be # constant time lookups when they call this method. applicable_metadata = applicable_metadata_from(metadata) if applicable_metadata.any? { |k, _| @proc_keys.include?(k) } # It's unsafe to memoize lookups involving procs (since they can # be non-deterministic), so we skip the memoization in this case. find_items_for(applicable_metadata) else @memoized_lookups[applicable_metadata] end end
# File lib/rspec/core/metadata_filter.rb, line 170 def prepend(item, metadata) super handle_mutation(metadata) end
# File lib/rspec/core/metadata_filter.rb, line 205 def applicable_metadata_from(metadata) MetadataFilter.silence_metadata_example_group_deprecations do @applicable_keys.inject({}) do |hash, key| # :example_group is treated special here because... # - In RSpec 2, example groups had an `:example_group` key # - In RSpec 3, that key is deprecated (it was confusing!). # - The key is not technically present in an example group metadata hash # (and thus would fail the `metadata.key?(key)` check) but a value # is provided when accessed via the hash's `default_proc` # - Thus, for backwards compatibility, we have to explicitly check # for `:example_group` here if it is one of the keys being used to # filter. hash[key] = metadata[key] if metadata.key?(key) || key == :example_group hash end end end
# File lib/rspec/core/metadata_filter.rb, line 199 def handle_mutation(metadata) @applicable_keys.merge(metadata.keys) @proc_keys.merge(proc_keys_from metadata) @memoized_lookups.clear end
# File lib/rspec/core/metadata_filter.rb, line 223 def proc_keys_from(metadata) metadata.each_with_object([]) do |(key, value), to_return| to_return << key if Proc === value end end