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

Inherits:
Base
  • Object
show all
Extended by:
AutoCorrector
Includes:
RangeHelp
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 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`

Examples:

# 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

Constant Summary collapse

MSG = 
'Use `%<new_method_name>s` instead of `each` to map elements into an array.'

Constants inherited from Base

Base::RESTRICT_ON_SEND

Instance Attribute Summary

Attributes inherited from Base

#config, #processed_source

Class Method Summary collapse

Instance Method Summary collapse

Methods included from AutoCorrector

support_autocorrect?

Methods inherited from Base

#active_support_extensions_enabled?, #add_global_offense, #add_offense, #always_autocorrect?, autocorrect_incompatible_with, badge, #begin_investigation, callbacks_needed, #callbacks_needed, #config_to_allow_offenses, #config_to_allow_offenses=, #contextual_autocorrect?, #cop_config, cop_name, #cop_name, department, documentation_url, exclude_from_registry, #excluded_file?, #external_dependency_checksum, inherited, #initialize, #inspect, lint?, match?, #message, #offenses, #on_investigation_end, #on_new_investigation, #on_other_file, #parse, #parser_engine, #ready, #relevant_file?, requires_gem, #string_literals_frozen_by_default?, support_autocorrect?, support_multiple_source?, #target_rails_version, #target_ruby_version

Methods included from ExcludeLimit

#exclude_limit

Methods included from AutocorrectLogic

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #autocorrect_with_disable_uncorrectable?, #correctable?, #disable_uncorrectable?, #safe_autocorrect?

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

silence_warnings

Constructor Details

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

Class Method Details

.joining_forces ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 105

def self.joining_forces
  VariableForce
end

Instance Method Details

#after_leaving_scope(scope, _variable_table) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 109

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

#each_block_with_push?(node) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 72

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

#empty_array_asgn?(node) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 81

def_node_matcher :empty_array_asgn?, <<~PATTERN
  (
    lvasgn _ {
      (array)
      (send (const {nil? cbase} :Array) :[])
      (send (const {nil? cbase} :Array) :new (array)?)
      (send nil? :Array (array))
    }
  )
PATTERN

#empty_array_tap(node) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 93

def_node_matcher :empty_array_tap, <<~PATTERN
  ^^$(
    block
      (send (array) :tap)
      (args (arg _))
      ...
  )
PATTERN

#lvar_ref?(node, name) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 103

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

#on_block(node) ⇒ Object Also known as: on_numblock 



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# 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

#suitable_argument_node?(node) ⇒ Object 



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# File 'lib/rubocop/cop/style/map_into_array.rb', line 67

def_node_matcher :suitable_argument_node?, <<-PATTERN
  !{splat forwarded-restarg forwarded-args (hash (forwarded-kwrestarg)) (block-pass nil?)}
PATTERN