#!/usr/bin/ruby
# -*- coding: utf-8 -*-

=begin
snake_case → camelCase 변환
=end

str = "hello_world"

puts str.split("_")
        .map { |s| s.capitalize}
        .join

# ---

x = str.gsub(/_[a-z]/) do |s|
  s.to_s.delete("_").upcase
end
puts x