We'll cover when and how to use string interpolation.

1. Interpolate variables into strings

You're a party planner for Beyonce's 35th birthday and you're using Ruby to help you out with the arrangements. There is a variable called num_of_attendees and since she's very popular, this variable points to the integer 547. You try and print the value of num_of_attendees to the screen with the code below:

puts "There are num_of_attendees people coming to Beyonce's birthday party."

You expect this to print "There are 547 people coming to Beyonce's birthday party" but instead it prints "There are num_of_attendees people coming to Beyonce's birthday party." Why is this?

Well, that's because variables need to be interpolated inside a string to get their value, and not just referenced by their name, to print to the screen.

To interpolate, you wrap the variable like #{this}.

Let's try again:

puts "There are #{num_of_attendees} people coming to Beyonce's birthday party."

This prints There are 547 people coming to Beyonce's birthday party.. Yay!

Let's drop into IRB and copy and paste the code from the following example.

Let's say you have a super hard question on your biology test asking you to identify the technical term for a group of flamingos.

answer = "< fill in your answer here >"
puts "A group of flamingos is called a #{answer}."

Now, set the answer variable equal to "flamboyance" and run the following code in IRB:

answer = "flamboyance"
puts "A group of flamingos is called a #{answer}."

This prints A group of flamingos is called a flamboyance. to the screen.

Note that here you're declaring the variable answer before calling puts. You need to do it in this order, because our program is read by the computer sequentially. When your computer gets to #{answer}, it won't know what that is if answer isn't defined yet.

Some Rubyists write this another way, like this:

answer = "Flamboyance"
puts "A group of flamingos is called a " + answer + "."

There's debate about the best practice but most people at Learn think the first way looks nicer and is easier for your fellow programmers to read.

Interpolation will only work on Strings wrapped in double quotes "". Single quotes: '' do not support string interpolation, so running:

answer = 'Flamboyance'
puts 'A group of flamingos is called a #{answer}.'

Will just print A group of flamingos is called a #{answer}.

If you were committed to using single quotes in such a case, it would be the right time to use the alternative method ('A group of flamingos is called a ' + answer + '.') which would work just fine.

Just to clarify, this only applies to puts and other Ruby methods; it does NOT apply to variables. That is, answer can equal "Flamboyance" (double quotes) or 'Flamboyance' (single quotes) without affecting string interpolation.

View String Interpolation on Learn.co and start learning to code for free.

View String Interpolation on Learn.co and start learning to code for free.