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Contents
# frozen_string_literal: true
module RuboCop
module Cop
module Performance
# In Ruby 2.3 or later, use unary plus operator to unfreeze a string
# literal instead of `String#dup` and `String.new`.
# Unary plus operator is faster than `String#dup`.
#
# Note: `String.new` (without operator) is not exactly the same as `+''`.
# These differ in encoding. `String.new.encoding` is always `ASCII-8BIT`.
# However, `(+'').encoding` is the same as script encoding(e.g. `UTF-8`).
# So, if you expect `ASCII-8BIT` encoding, disable this cop.
#
# @example
# # bad
# ''.dup
# "something".dup
# String.new
# String.new('')
# String.new('something')
#
# # good
# +'something'
# +''
class UnfreezeString < Cop
extend TargetRubyVersion
minimum_target_ruby_version 2.3
MSG = 'Use unary plus to get an unfrozen string literal.'.freeze
def_node_matcher :dup_string?, <<-PATTERN
(send {str dstr} :dup)
PATTERN
def_node_matcher :string_new?, <<-PATTERN
{
(send (const nil? :String) :new {str dstr})
(send (const nil? :String) :new)
}
PATTERN
def on_send(node)
add_offense(node) if dup_string?(node) || string_new?(node)
end
end
end
end
end
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