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# frozen_string_literal: true
module RuboCop
module Cop
module Style
# Identifies usages of `arr[0]` and `arr[-1]` and suggests to change
# them to use `arr.first` and `arr.last` instead.
#
# The cop is disabled by default due to safety concerns.
#
# @safety
# This cop is unsafe because `[0]` or `[-1]` can be called on a Hash,
# which returns a value for `0` or `-1` key, but changing these to use
# `.first` or `.last` will return first/last tuple instead. Also, String
# does not implement `first`/`last` methods.
#
# @example
# # bad
# arr[0]
# arr[-1]
#
# # good
# arr.first
# arr.last
# arr[0] = 2
# arr[0][-2]
#
class ArrayFirstLast < Base
extend AutoCorrector
MSG = 'Use `%<preferred>s`.'
RESTRICT_ON_SEND = %i[[]].freeze
# rubocop:disable Metrics/AbcSize
def on_send(node)
return unless node.arguments.size == 1 && node.first_argument.int_type?
value = node.first_argument.value
return unless [0, -1].include?(value)
node = innermost_braces_node(node)
return if node.parent && brace_method?(node.parent)
preferred = (value.zero? ? 'first' : 'last')
add_offense(node.loc.selector, message: format(MSG, preferred: preferred)) do |corrector|
corrector.replace(node.loc.selector, ".#{preferred}")
end
end
# rubocop:enable Metrics/AbcSize
private
def innermost_braces_node(node)
node = node.receiver while node.receiver.send_type? && node.receiver.method?(:[])
node
end
def brace_method?(node)
node.send_type? && (node.method?(:[]) || node.method?(:[]=))
end
end
end
end
end
Version data entries
32 entries across 32 versions & 7 rubygems