Class: RuboCop::Cop::Performance::RedundantStringChars

Relationships & Source Files
Super Chains via Extension / Inclusion / Inheritance
Class Chain: self, AutoCorrector, Base
Instance Chain: self, RangeHelp, Base
Inherits:	Base Object Base RuboCop::Cop::Performance::RedundantStringChars
Defined in:	lib/rubocop/cop/performance/redundant_string_chars.rb

Overview

Checks for redundant String#chars.

Examples:

# bad
str.chars[0..2]
str.chars.slice(0..2)
str.chars.last

# good
str[0..2].chars

# bad
str.chars.first
str.chars.first(2)

# good
str[0]
str[0...2].chars
str[-1]

# bad
str.chars.take(2)
str.chars.length
str.chars.size
str.chars.empty?

# good
str[0...2].chars
str.length
str.size
str.empty?

# For example, if the receiver is an empty string, it will be incompatible.
# If a negative value is specified for the receiver, {nil} is returned.
str.chars.last(2) # Incompatible with {str[-2..-1].chars}.
str.chars.drop(2) # Incompatible with {str[2..-1].chars}.

Constant Summary

MSG =
# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 47
```
'Use `%<good_method>s` instead of `%<bad_method>s`.'
```
RESTRICT_ON_SEND =
# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 48
```
%i[[] slice first last take length size empty?].freeze
```

Instance Method Summary

#on_send(node)
#build_bad_method(method, args) private
#build_call_args(call_args_node) private
#build_good_method(method, args) private
#build_good_method_for_brackets_or_first_method(method, args) private
#build_message(method, args) private
#correction_range(receiver, node) private
#offense_range(receiver, node) private

Instance Method Details

#build_bad_method(method, args) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 112


def build_bad_method(method, args)
  case method
  when :[]
    "chars[#{build_call_args(args)}]"
  else
    if args.any?
      "chars.#{method}(#{build_call_args(args)})"
    else
      "chars.#{method}"
    end
  end
end

#build_call_args(call_args_node) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 125


def build_call_args(call_args_node)
  call_args_node.map(&:source).join(', ')
end

#build_good_method(method, args) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 85


def build_good_method(method, args)
  case method
  when :slice
    "[#{build_call_args(args)}].chars"
  when :[], :first
    build_good_method_for_brackets_or_first_method(method, args)
  when :last
    '[-1]'
  when :take
    "[0...#{args.first.source}].chars"
  else
    ".#{method}"
  end
end

#build_good_method_for_brackets_or_first_method(method, args) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 100


def build_good_method_for_brackets_or_first_method(method, args)
  first_arg = args.first

  if first_arg&.range_type?
    "[#{build_call_args(args)}].chars"
  elsif method == :first && args.any?
    "[0...#{args.first.source}].chars"
  else
    first_arg ? "[#{first_arg.source}]" : '[0]'
  end
end

#build_message(method, args) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 79


def build_message(method, args)
  good_method = build_good_method(method, args)
  bad_method = build_bad_method(method, args)
  format(MSG, good_method: good_method, bad_method: bad_method)
end

#correction_range(receiver, node) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 75


def correction_range(receiver, node)
  range_between(receiver.loc.dot.begin_pos, node.source_range.end_pos)
end

#offense_range(receiver, node) (private)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 71


def offense_range(receiver, node)
  range_between(receiver.loc.selector.begin_pos, node.source_range.end_pos)
end

#on_send(node)

[ GitHub ]

# File 'lib/rubocop/cop/performance/redundant_string_chars.rb', line 54


def on_send(node)
  return unless (receiver, method, args = redundant_chars_call?(node))
  return if method == :last && !args.empty?

  range = offense_range(receiver, node)
  message = build_message(method, args)

  add_offense(range, message: message) do |corrector|
    range = correction_range(receiver, node)
    replacement = build_good_method(method, args)

    corrector.replace(range, replacement)
  end
end