Triple single quote vs triple double quote in Ruby

Question

Why might you use ''' instead of """, as in Learn Ruby the Hard Way, Chapter 10 Study Drills?

Answer 1

There are no triple quotes in Ruby.

Two String literals which are juxtaposed are parsed as a single String literal. So,

'Hello' 'World'
#=> "HelloWorld"

is the same as

'HelloWorld'
#=> "HelloWorld"

And

'' 'Hello' ''
#=> "Hello"

is the same as

'''Hello'''
#=> "Hello"

is the same as

'Hello'
#=> "Hello"

Since adding an empty string literal does not change the result, you can add as many empty strings as you want:

""""""""""""'''''Hello'''''''''
#=> "Hello"

There are no special rules for triple single quotes vs. triple double quotes, because there are no triple quotes. The rules are simply the same as for quotes.

Answer 2

I assume the author confused Ruby and Python, because a triple-quote will not work in Ruby the way author thought it would. It'll just work like three separate strings ('' '' '').

For multi-line strings one could use:

%q{
 your text
 goes here
}
 => "\n     your text\n     goes here\n    "

or %Q{} if you need string interpolation inside.

Answer 3

Triple-quotes ''' are the same as single quotes ' in that they don't interpolate any #{} sequences, escape characters (like "\n"), etc.

Triple-double-quotes (ugh) """ are the same as double-quotes " in that they do interpolation and escape sequences.

This is further down on the same page you linked.

The triple-quoted versions """ ''' allows for multi-line strings... as does the singly-quoted ' and ", so I don't know why both are available.

Answer 4

In Ruby """ supports interpolation, ''' does not.

Rubyists use triple quotes for multi-line strings (similar to 'heredocs').

You could just as easily use one of these characters.

Just like normal strings the double quotes will allow you to use variables inside of your strings (also known as 'interpolation').

Save this to a file called multiline_example.rb and run it:

interpolation = "(but this one can use interpolation)"

single = '''
This is a multi-line string.
'''

double = """
This is also a multi-line string #{interpolation}.
"""

puts single
puts double

This is the output:

$ ruby multiline_string_example.rb

This is a multi-line string.

This is also a multi-line string (but this one can use interpolation).

$

Now try it the other way around:

nope = "(this will never get shown)"

single = '''
This is a multi-line string #{nope}.
'''

double = """
This is also a multi-line string.
"""

puts single
puts double

You'll get this output:

$ ruby multiline_example.rb

This is a multi-line string #{nope}.

This is also a multi-line string.

$

Note that in both examples you got some extra newlines in your output. That's because multiline strings keep any newlines inside them, and puts adds a newline to every string.