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Class: RuboCop::Cop::Style::MapIntoArray

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain:
self, ::RuboCop::Cop::AutoCorrector, ::RuboCop::Cop::Base, ::RuboCop::ExcludeLimit, NodePattern::Macros, RuboCop::AST::Sexp
Instance Chain:
Inherits: RuboCop::Cop::Base
Defined in: lib/rubocop/cop/style/map_into_array.rb

Overview

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 a local variable initialized as an empty array and referred to only by the pushing operation. This is because, if not, it’s challenging to statically guarantee that the mapping destination variable remains an empty array:
ret = []
src.each { |e| ret << e * 2 } # `<<` method may mutate `ret`

dest = []
src.each { |e| dest << transform(e, dest) } # `transform` method may mutate `dest`

Examples:

# bad
dest = []
src.each { |e| dest << e * 2 }
dest

# good
dest = src.map { |e| e * 2 }

# good - contains another operation
dest = []
src.each { |e| dest << e * 2; puts e }
dest

Cop Safety Information:

  • 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).

Constant Summary

::RuboCop::Cop::Base - Inherited

EMPTY_OFFENSES, RESTRICT_ON_SEND

::RuboCop::Cop::RangeHelp - Included

BYTE_ORDER_MARK, NOT_GIVEN

Class Attribute Summary

::RuboCop::Cop::AutoCorrector - Extended

::RuboCop::Cop::Base - Inherited

.gem_requirements, .lint?,
.support_autocorrect?

Returns if class supports autocorrect.

.support_multiple_source?

Override if your cop should be called repeatedly for multiple investigations Between calls to on_new_investigation and on_investigation_end, the result of processed_source will remain constant.

Class Method Summary

::RuboCop::Cop::Base - Inherited

.autocorrect_incompatible_with

List of cops that should not try to autocorrect at the same time as this cop.

.badge

Naming.

.callbacks_needed, .cop_name, .department,
.documentation_url

Returns an url to view this cops documentation online.

.exclude_from_registry

Call for abstract Cop classes.

.inherited,
.joining_forces

Override and return the Force class(es) you need to join.

.match?

Returns true if the cop name or the cop namespace matches any of the given names.

.new,
.requires_gem

Register a version requirement for the given gem name.

.restrict_on_send

::RuboCop::ExcludeLimit - Extended

exclude_limit

Sets up a configuration option to have an exclude limit tracked.

transform

Instance Attribute Summary

Instance Method Summary

::RuboCop::Cop::RangeHelp - Included

#add_range, #column_offset_between,
#contents_range

A range containing only the contents of a literal with delimiters (e.g.

#directions,
#effective_column

Returns the column attribute of the range, except if the range is on the first line and there’s a byte order mark at the beginning of that line, in which case 1 is subtracted from the column value.

#final_pos, #move_pos, #move_pos_str, #range_between, #range_by_whole_lines, #range_with_comments, #range_with_comments_and_lines, #range_with_surrounding_comma, #range_with_surrounding_space, #source_range

::RuboCop::Cop::Base - Inherited

#add_global_offense

Adds an offense that has no particular location.

#add_offense

Adds an offense on the specified range (or node with an expression) Unless that offense is disabled for this range, a corrector will be yielded to provide the cop the opportunity to autocorrect the offense.

#begin_investigation

Called before any investigation.

#callbacks_needed,
#cop_config

Configuration Helpers.

#cop_name, #excluded_file?,
#external_dependency_checksum

This method should be overridden when a cop’s behavior depends on state that lives outside of these locations:

#inspect
#message

Gets called if no message is specified when calling add_offense or add_global_offense Cops are discouraged to override this; instead pass your message directly.

#name

Alias for Base#cop_name.

#offenses,
#on_investigation_end

Called after all on_…​

#on_new_investigation

Called before all on_…​

#on_other_file

Called instead of all on_…​

#parse

There should be very limited reasons for a Cop to do it’s own parsing.

#parser_engine,
#ready

Called between investigations.

#relevant_file?, #target_rails_version, #target_ruby_version, #annotate, #apply_correction, #attempt_correction,
#callback_argument

Reserved for Cop::Cop.

#complete_investigation

Called to complete an investigation.

#correct, #current_corrector,
#current_offense_locations

Reserved for Commissioner:

#current_offenses, #currently_disabled_lines, #custom_severity, #default_severity, #disable_uncorrectable, #enabled_line?, #file_name_matches_any?, #find_message, #find_severity, #range_for_original, #range_from_node_or_range,
#reset_investigation

Actually private methods.

#use_corrector

::RuboCop::Cop::AutocorrectLogic - Included

::RuboCop::Cop::IgnoredNode - Included

Constructor Details

This class inherits a constructor from RuboCop::Cop::Base

Class Method Details

.joining_forces

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 71

def self.joining_forces
  VariableForce
end

Instance Method Details

#after_leaving_scope(scope, _variable_table)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 75

def after_leaving_scope(scope, _variable_table)
  (@scopes ||= []) << scope
end

#correct_push_node(corrector, push_node) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 155

def correct_push_node(corrector, push_node)
  range = push_node.source_range
  arg_range = push_node.first_argument.source_range

  corrector.remove(range_between(range.begin_pos, arg_range.begin_pos))
  corrector.remove(range_between(arg_range.end_pos, range.end_pos))
end

#correct_return_value_handling(corrector, block, dest_var) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 163

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

#dest_used_only_for_mapping?(block, dest_var, asgn) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 108

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

#each_block_with_push?(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 57

def_node_matcher :each_block_with_push?, <<-PATTERN
  [
    ^({begin kwbegin} ...)
    ({block numblock} (send !{nil? self} :each) _
      (send (lvar _) {:<< :push :append} _))
  ]
PATTERN

#empty_array_asgn?(node)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 66

def_node_matcher :empty_array_asgn?, '(lvasgn _ (array))'

#find_closest_assignment(block, dest_var) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 102

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

#find_dest_var(block) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 94

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

#lvar_ref?(node, name)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 69

def_node_matcher :lvar_ref?, '(lvar %1)'

#new_method_name (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 127

def new_method_name
  default = 'map'
  alternative = config.for_cop('Style/CollectionMethods').dig('PreferredMethods', default)
  alternative || default
end

#on_block(node) Also known as: #on_numblock

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 79

def on_block(node)
  return unless each_block_with_push?(node)

  dest_var = find_dest_var(node)
  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)

  register_offense(node, dest_var, asgn)
end

#on_numblock(node)

Alias for #on_block.

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 90

alias on_numblock on_block

#register_offense(block, dest_var, asgn) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 116

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)
    remove_assignment(corrector, asgn)
    correct_push_node(corrector, block.body)
    correct_return_value_handling(corrector, block, dest_var)
  end
end

#remove_assignment(corrector, asgn) (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 148

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

#return_value_used?(node) ⇒ Boolean (private)

[ GitHub ]

  
# File 'lib/rubocop/cop/style/map_into_array.rb', line 133

def return_value_used?(node)
  parent = node.parent

  case parent&.type
  when nil
    false
  when :begin, :kwbegin
    !node.right_sibling && return_value_used?(parent)
  when :block, :numblock
    !parent.void_context?
  else
    true
  end
end