class RuboCop::Cop::Style::ArrayFirstLast
Identifies usages of ‘arr` and `arr` 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]
Constants
- MSG
- RESTRICT_ON_SEND
Public Instance Methods
on_send(node)
click to toggle source
rubocop:disable Metrics/AbcSize
# File lib/rubocop/cop/style/array_first_last.rb, line 35 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
Private Instance Methods
brace_method?(node)
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# File lib/rubocop/cop/style/array_first_last.rb, line 58 def brace_method?(node) node.send_type? && (node.method?(:[]) || node.method?(:[]=)) end
innermost_braces_node(node)
click to toggle source
rubocop:enable Metrics/AbcSize
# File lib/rubocop/cop/style/array_first_last.rb, line 53 def innermost_braces_node(node) node = node.receiver while node.receiver.send_type? && node.receiver.method?(:[]) node end