Class: RuboCop::Cop::Performance::ChainArrayAllocation

Inherits:
Cop
  • Object
show all
Includes:
RangeHelp
Defined in:
lib/rubocop/cop/performance/chain_array_allocation.rb

Overview

This cop is used to identify usages of Each of these methods (‘compact`, `flatten`, `map`) will generate a new intermediate array that is promptly thrown away. Instead it is faster to mutate when we know it’s safe.

Examples:

# bad
array = ["a", "b", "c"]
array.compact.flatten.map { |x| x.downcase }
# good.
array = ["a", "b", "c"]
array.compact!
array.flatten!
array.map! { |x| x.downcase }
array

Constant Summary collapse

RETURN_NEW_ARRAY_WHEN_ARGS =

These methods return a new array but only sometimes. They must be called with an argument. For example:

[1,2].first    # => 1
[1,2].first(1) # => [1]

':first :last :pop :sample :shift '.freeze
RETURNS_NEW_ARRAY_WHEN_NO_BLOCK =

These methods return a new array only when called without a block.

':zip :product '.freeze
ALWAYS_RETURNS_NEW_ARRAY =

These methods ALWAYS return a new array after they’re called it’s safe to mutate the the resulting array

':* :+ :- :collect :compact :drop '\
':drop_while :flatten :map :reject ' \
':reverse :rotate :select :shuffle :sort ' \
':take :take_while :transpose :uniq ' \
':values_at :| '.freeze
HAS_MUTATION_ALTERNATIVE =

These methods have a mutation alternative. For example :collect can be called as :collect!

':collect :compact :flatten :map :reject '\
':reverse :rotate :select :shuffle :sort '\
':uniq '.freeze
MSG = 
'Use unchained `%<method>s!` and `%<second_method>s!` '\
'(followed by `return array` if required) instead of chaining '\
'`%<method>s...%<second_method>s`.'.freeze

Constants included from Util

Util::LITERAL_REGEX

Instance Attribute Summary

Attributes inherited from Cop

#config, #corrections, #offenses, #processed_source

Instance Method Summary collapse

Methods inherited from Cop

#add_offense, all, autocorrect_incompatible_with, badge, #config_to_allow_offenses, #config_to_allow_offenses=, #cop_config, cop_name, #cop_name, #correct, department, #duplicate_location?, #excluded_file?, #find_location, #highlights, inherited, #initialize, #join_force?, lint?, match?, #message, #messages, non_rails, #parse, qualified_cop_name, #relevant_file?, #target_rails_version, #target_ruby_version

Methods included from AST::Sexp

#s

Methods included from NodePattern::Macros

#def_node_matcher, #def_node_search, #node_search, #node_search_all, #node_search_body, #node_search_first

Methods included from AutocorrectLogic

#autocorrect?, #autocorrect_enabled?, #autocorrect_requested?, #support_autocorrect?

Methods included from IgnoredNode

#ignore_node, #ignored_node?, #part_of_ignored_node?

Methods included from Util

begins_its_line?, comment_line?, double_quotes_required?, escape_string, first_part_of_call_chain, interpret_string_escapes, line_range, needs_escaping?, on_node, parentheses?, same_line?, to_string_literal, to_supported_styles, tokens, trim_string_interporation_escape_character

Methods included from PathUtil

absolute?, chdir, hidden_dir?, hidden_file_in_not_hidden_dir?, match_path?, pwd, relative_path, reset_pwd, smart_path

Constructor Details

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

Instance Method Details

#on_send(node) ⇒ Object 



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# File 'lib/rubocop/cop/performance/chain_array_allocation.rb', line 62

def on_send(node)
  flat_map_candidate?(node) do |fm, sm, _|
    range = range_between(
      node.loc.dot.begin_pos,
      node.source_range.end_pos
    )
    add_offense(
      node,
      location: range,
      message: format(MSG, method: fm, second_method: sm)
    )
  end
end