Heredoc with Ruby

In Ruby, it is possible to use a Heredoc in order to write a multiline strings.

This is done just like in Unix shells, with the important difference that no space should come between the heredoc identifier and the double carret (<<) because Ruby uses thoses as well.

result = <<HEREDOC
First line
Second line
HEREDOC

The identifier (here, HEREDOC) can be whatever you want but all-uppercase identifiers are generally used.

One inconvenience with heredoc is that, as they preserve spaces and indentation, writting heredoc in Ruby can results in ugly and badly indented code:

class TicketMachine
  def error
    <<-HEREDOC
This ticket is #{travel_price} yens.
Please insert #{insufficient_funds} yens.
Thank you.
    HEREDOC
  end
end

If we had indented our multiline strings correctly, the indentation would have ben output as is, which is not what we want.

To have the message aligned against the left amrgin, we can use…

The Squiggly Heredoc

Since Ruby 2.3, we have a new heredoc syntax called the squiggly heredoc. Beside a funny name, it strips the leading whitespace in order to let you write nicer code:

class TicketMachine
  def error
    <<~HEREDOC
      This ticket is #{travel_price} yens.
      Please insert #{insufficient_funds} yens.
      Thank you.
    HEREDOC
  end
end

The only difference beside the now well indented multiline strings, is the use of the tilda: <<~.

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