[ruby] Multi-Line Comments in Ruby?

How can I comment multiple lines in Ruby?

Despite the existence of =begin and =end, the normal and a more correct way to comment is to use #'s on each line. If you read the source of any ruby library, you will see that this is the way multi-line comments are done in almost all cases.

=begin
(some code here)
=end

and

# This code
# on multiple lines
# is commented out

are both correct. The advantage of the first type of comment is editability—it's easier to uncomment because fewer characters are deleted. The advantage of the second type of comment is readability—reading the code line by line, it's much easier to tell that a particular line has been commented out. Your call but think about who's coming after you and how easy it is for them to read and maintain.

=begin
My 
multiline
comment
here
=end

  def idle
    <<~aid
    This is some description of what idle does.

    It does nothing actually, it's just here to show an example of multiline
    documentation. Thus said, this is something that is more common in the
    python community. That's an important point as it's good to also fit the
    expectation of your community of work. Now, if you agree with your team to
    go with a solution like this one for documenting your own base code, that's
    fine: just discuss about it with them first.

    Depending on your editor configuration, it won't be colored like a comment,
    like those starting with a "#". But as any keyword can be used for wrapping
    an heredoc, it is easy to spot anyway. One could even come with separated
    words for different puposes, so selective extraction for different types of
    documentation generation would be more practical. Depending on your editor,
    you possibly could configure it to use the same syntax highlight used for
    monoline comment when the keyword is one like aid or whatever you like.

    Also note that the squiggly-heredoc, using "~", allow to position
    the closing term with a level of indentation. That avoids to break the visual reading flow, unlike this far too long line.
    aid
  end

Note that at the moment of the post, the stackoverflow engine doesn't render syntax coloration correctly. Testing how it renders in your editor of choice is let as an exercise. ;)

#!/usr/bin/env ruby

=begin
Between =begin and =end, any number
of lines may be written. All of these
lines are ignored by the Ruby interpreter.
=end

puts "Hello world!"

Here is an example :

=begin 
print "Give me a number:"
number = gets.chomp.to_f

total = number * 10
puts  "The total value is : #{total}"

=end

Everything you place in between =begin and =end will be treated as a comment regardless of how many lines of code it contains between.

Note: Make sure there is no space between = and begin:

• Correct: =begin
• Wrong: = begin

Using either:

=begin
This
is
a
comment
block
=end

or

# This
# is
# a
# comment
# block

are the only two currently supported by rdoc, which is a good reason to use only these I think.

=begin comment line 1 comment line 2 =end make sure =begin and =end is the first thing on that line (no spaces)

In case someone is looking for a way to comment multiple lines in a html template in Ruby on Rails, there might be a problem with =begin =end, for instance:

<%
=begin
%>
  ... multiple HTML lines to comment out
  <%= image_tag("image.jpg") %>
<%
=end
%>

will fail because of the %> closing the image_tag.

In this case, maybe it is arguable whether this is commenting out or not, but I prefer to enclose the undesired section with an "if false" block:

<% if false %>
  ... multiple HTML lines to comment out
  <%= image_tag("image.jpg") %>
<% end %>

This will work.