class RuboCop::Cop::Style::MapIntoArray
Checks for usages of ‘each` with `<<`, `push`, or `append` which can be replaced by `map`.
If ‘PreferredMethods` is configured for `map` in `Style/CollectionMethods`, this cop uses the specified method for replacement.
NOTE: The return value of ‘Enumerable#each` is `self`, whereas the return value of `Enumerable#map` is an `Array`. They are not autocorrected when a return value could be used because these types differ.
NOTE: It only detects when the mapping destination is either:
-
a local variable initialized as an empty array and referred to only by the
pushing operation;
-
or, if it is the single block argument to a ‘[].tap` block.
This is because, if not, it’s challenging to statically guarantee that the mapping destination variable remains an empty array:
- source,ruby
ret = [] src.each { |e| ret << e * 2 } # ‘<<` method may mutate `ret`
dest = [] src.each { |e| dest << transform(e, dest) } # ‘transform` method may mutate `dest`
@safety
This cop is unsafe because not all objects that have an `each` method also have a `map` method (e.g. `ENV`). Additionally, for calls with a block, not all objects that have a `map` method return an array (e.g. `Enumerator::Lazy`).
@example
# bad dest = [] src.each { |e| dest << e * 2 } dest # good dest = src.map { |e| e * 2 } # bad [].tap do |dest| src.each { |e| dest << e * 2 } end # good dest = src.map { |e| e * 2 } # good - contains another operation dest = [] src.each { |e| dest << e * 2; puts e } dest
Constants
- MSG
Public Class Methods
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 105 def self.joining_forces VariableForce end
Public Instance Methods
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 109 def after_leaving_scope(scope, _variable_table) (@scopes ||= []) << scope end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 113 def on_block(node) return unless each_block_with_push?(node) dest_var = find_dest_var(node) if offending_empty_array_tap?(node, dest_var) asgn = dest_var.declaration_node else return unless (asgn = find_closest_assignment(node, dest_var)) return unless empty_array_asgn?(asgn) return unless dest_used_only_for_mapping?(node, dest_var, asgn) end register_offense(node, dest_var, asgn) end
Private Instance Methods
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 214 def correct_push_node(corrector, push_node) arg_node = push_node.first_argument range = push_node.source_range arg_range = arg_node.source_range corrector.wrap(arg_node, '{ ', ' }') if arg_node.hash_type? && !arg_node.braces? corrector.remove(range_between(range.begin_pos, arg_range.begin_pos)) corrector.remove(range_between(arg_range.end_pos, range.end_pos)) end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 224 def correct_return_value_handling(corrector, block, dest_var) next_node = block.right_sibling if lvar_ref?(next_node, dest_var.name) corrector.remove(range_with_surrounding_space(next_node.source_range, side: :left)) end corrector.insert_before(block, "#{dest_var.name} = ") end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 157 def dest_used_only_for_mapping?(block, dest_var, asgn) range = asgn.source_range.join(block.source_range) asgn.parent.equal?(block.parent) && dest_var.references.one? { |r| range.contains?(r.node.source_range) } && dest_var.assignments.one? { |a| range.contains?(a.node.source_range) } end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 151 def find_closest_assignment(block, dest_var) dest_var.assignments.reverse_each.lazy.map(&:node).find do |node| node.source_range.end_pos < block.source_range.begin_pos end end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 134 def find_dest_var(block) node = block.body.receiver name = node.children.first candidates = @scopes.lazy.filter_map { |s| s.variables[name] } candidates.find { |v| v.references.any? { |n| n.node.equal?(node) } } end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 182 def new_method_name default = 'map' alternative = config.for_cop('Style/CollectionMethods').dig('PreferredMethods', default) alternative || default end
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# File lib/rubocop/cop/style/map_into_array.rb, line 142 def offending_empty_array_tap?(node, dest_var) return false unless (tap_block_node = empty_array_tap(dest_var.declaration_node)) # A `tap` block only offends if the array push is the only thing in it; # otherwise we cannot guarantee that the block variable is still an empty # array when pushed to. tap_block_node.body == node end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 165 def register_offense(block, dest_var, asgn) add_offense(block, message: format(MSG, new_method_name: new_method_name)) do |corrector| next if return_value_used?(block) corrector.replace(block.send_node.selector, new_method_name) if (tap_block_node = empty_array_tap(dest_var.declaration_node)) remove_tap(corrector, block, tap_block_node) else remove_assignment(corrector, asgn) end correct_push_node(corrector, block.body) correct_return_value_handling(corrector, block, dest_var) end end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 201 def remove_assignment(corrector, asgn) range = range_with_surrounding_space(asgn.source_range, side: :right) range = range_with_surrounding_space(range, side: :right, newlines: false) corrector.remove(range) end
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# File lib/rubocop/cop/style/map_into_array.rb, line 208 def remove_tap(corrector, node, block_node) range = range_between(block_node.source_range.begin_pos, node.source_range.begin_pos) corrector.remove(range) corrector.remove(range_with_surrounding_space(block_node.loc.end, side: :left)) end
Source
# File lib/rubocop/cop/style/map_into_array.rb, line 188 def return_value_used?(node) parent = node.parent case parent&.type when nil false when :begin, :kwbegin !node.right_sibling && return_value_used?(parent) else !parent.respond_to?(:void_context?) || !parent.void_context? end end