Strings

• Prefer string interpolation and string formatting instead of string concatenation: ^[link]

  # bad
  email_with_name = user.name + " <" + user.email + ">"
  
  # good
  email_with_name = "#{user.name} <#{user.email}>"
  
  # good
  email_with_name = format("%s <%s>", user.name, user.email)
  

• With interpolated expressions, there should be no padded-spacing inside the braces. ^[link]

  # bad
  "From: #{ user.first_name }, #{ user.last_name }"
  
  # good
  "From: #{user.first_name}, #{user.last_name}"
  

• Prefer double-quotes unless your string literal contains " or escape characters you want to suppress. It's less hassle if you later need to add escapes, use interpolation, or insert an apostrophe. ^[link]

  # bad
  name = 'Bozhidar'
  
  # good
  name = "Bozhidar"
  

• Don't use the character literal syntax ?x. Since Ruby 1.9 it's basically redundant: ?x would interpreted as "x" (a string with a single character in it). ^[link]

  # bad
  char = ?c
  
  # good
  char = "c"
  

• Don't leave out {} around instance and global variables being interpolated into a string. ^[link]

  class Person
    attr_reader :first_name, :last_name
  
    def initialize(first_name, last_name)
      @first_name = first_name
      @last_name = last_name
    end
  
    # bad:  valid, but awkward
    def to_s
      "#@first_name #@last_name"
    end
  
    # good
    def to_s
      "#{@first_name} #{@last_name}"
    end
  end
  
  $global = 0
  # bad
  puts "$global = #$global"
  
  # good
  puts "$global = #{$global}"
  

• Don't use Object#to_s on interpolated objects. It's invoked on them automatically. ^[link]

  # bad
  message = "This is the #{result.to_s}."
  
  # good
  message = "This is the #{result}."
  

• Avoid using String#+ when you need to construct large data chunks. Instead, use String#<<. Concatenation mutates the string instance in-place and is always faster than String#+, which creates a bunch of new string objects. ^[link]

  # bad
  html = ""
  html += "<h1>Page title</h1>"
  
  paragraphs.each do |paragraph|
    html += "<p>#{paragraph}</p>"
  end
  
  # good and also fast
  html = ""
  html << "<h1>Page title</h1>"
  
  paragraphs.each do |paragraph|
    html << "<p>#{paragraph}</p>"
  end
  

• Don't use String#gsub in scenarios in which you can use a faster more specialized alternative. ^[link]

    url = "http://example.com"
    str = "lisp-case-rules"
  
    # bad
    url.gsub("http://", "https://")
    str.gsub("-", "_")
  
    # good
    url.sub("http://", "https://")
    str.tr("-", "_")
  

• When using heredocs for multi-line strings keep in mind the fact that they preserve leading whitespace by default. It's a good practice to employ Ruby 2.3's <<~ trimming heredoc syntax or use some margin indicator to trim the excessive whitespace. ^[link]

  # good:  requires Ruby 2.3+
  code = <<~END
    def test
      some_method
      other_method
    end
  END
  # => "def test\n  some_method\n  other_method\nend\n"
  
  # passable:  support older Ruby versions
  code = <<-END.gsub(/^\s+\|/, "")
    |def test
    |  some_method
    |  other_method
    |end
  END
  # => "def test\n  some_method\n  other_method\nend\n"