Interpolation Super Power

Objectives

1. Interpolate arbitrary code into a string
2. Interpolate elements of an array into a single string

Overview

We've talked about string interpolation, but let's review quickly. String interpolation allows us to evaluate Ruby code, and inject the return value into the middle of a string. Normally, we see something like this:

name = "Bob"

puts "Hello, #{name}"

# => "Hello, Bob"

We're not just limited to injecting simple variables, though. We can do slightly fancier things if we just think of the pound sign/curly braces (#{}) as delimiters that allow us to run arbitrary code in the middle of a string. For example, there is nothing preventing us from doing something like this:

puts "1 plus 1 is #{1 + 1}!"

# => "1 plus 1 is 2!"

Almost anything is fair game here. In fact, we're not even limited to just one interpolation per string. It's perfectly acceptable for me to do the following:

three = 2 + 1
name  = "Bob"

puts "1 plus 1 is #{1 + 1} and 1 plus 2 is #{three} and 2 times 2 is
#{2 * 2}. Oh, hey #{name}!"

# => "1 plus 1 is 2 and 1 plus 2 is 3 and 2 times 2 is 4. Oh, hey Bob!"

This means we can do some pretty awesome stuff! Let's say we wanted to print out a business card for our friend, Bob. We want it to look like this:

# => "Name: Bob, Age: 46, Occupation: Juggler"

At first blush, it might make sense to do something like this:

name       = "Bob"
age        = 46
occupation = "Juggler"

puts "Name: #{name}, Age: #{age}, Occupation: #{occupation}"

# => "Name: Bob, Age: 46, Occupation: Juggler"

But what if, now, we also want to print a business card for Stefani? With this pattern, we'd need to start creating a whole bunch of variables:

bob_name           = "Bob"
bob_age            = 46
bob_occupation     = "Juggler"
stefani_name       = "Stefani"
stefani_age        = 49
stefani_occupation = "Firefighter"

puts "Name: #{bob_name}, Age: #{bob_age}, Occupation: #{bob_occupation}"

# => "Name: Bob, Age: 46, Occupation: Juggler"

puts "Name: #{stefani_name}, Age: #{stefani_age}, Occupation:
#{stefani_occupation}"

# => "Name: Stefani, Age: 49, Occupation: Firefighter"

Three variables per person is going to get really, really messy once we want to print 5, 10, or 100 business cards. We can clean this up quite a bit by considering that name, age, and occupation really just comprise a list of attributes about a person. We have a really great data structure for representing lists in Ruby...an array!

With that in mind, let's represent our data as an array:

bob     = ["Bob", 46, "Juggler"]
stefani = ["Stefani", 49, "Firefighter"]

If we wanted to print out Bob's name, we'd do it like this:

name = bob[0]

puts name

# => "Bob"

There's an extra step there, though! As we know, we can run whatever Ruby code we want inside the #{} in a string. So we can just access the first element in the array directly within the string:

puts "#{bob[0]}"

# => "Bob"

This is going to clean up our business card printer quite a bit!

bob     = ["Bob", 46, "Juggler"]
stefani = ["Stefani", 49, "Firefighter"]

puts "Name: #{bob[0]}, Age: #{bob[1]}, Occupation: #{bob[2]}"

# => "Name: Bob, Age: 46, Occupation: Juggler"

puts "Name: #{stefani[0]}, Age: #{stefani[1]}, Occupation: #{stefani[2]}"

# => "Name: Stefani, Age: 49, Occupation: Firefighter"

Nice! But even this is a bit much. The fact that we have to repeat so much code is a pretty good sign that we need a printer method.

So let's do that! Let's make a method, #print_business_card, that accepts an array representing a person, and then prints out their business card. First, we'll create the basic method signature:

def print_business_card(person)
end

Now, let's re-use the code we've already written to print out the passed-in person's details:

def print_business_card(person)
  puts "Name: #{person[0]}, Age: #{person[1]}, Occupation: #{person[2]}"
end

Something is missing, though. Our people need a phone number. Let's change our people arrays to look like this:

bob = ["Bob", 46, "Juggler", "555-555-5555"]

And in our #print_business_card method, let's print that out on a second line:

def print_business_card(person)
  puts "Name: #{person[0]}, Age: #{person[1]}, Occupation: #{person[2]}"
  puts "Contact: #{person[3]}"
end

Now, let's use this! Let's print out business cards for Bob and Stefani:

bob     = ["Bob", 46, "Juggler", "555-555-5555"]
stefani = ["Stefani", 49, "Firefighter", "555-111-1111"]

print_business_card(bob)

# => "Name: Bob, Age: 46, Occupation: Juggler"
# => "Contact: 555-555-5555"

print_business_card(stefani)

# => "Name: Stefani, Age: 49, Occupation: Firefighter"
# => "Contact: 555-111-1111"

String interpolation is basically a super power. And like any good super power, mastery comes with practice! (That's how Superman got so good at flying, right?) Your turn!

Instructions

1. Define a method, #display_rainbow, in lib/display_rainbow.rb
2. #display_rainbow should print out the colors of the rainbow in the following format: "R: red, O: orange, Y: yellow, G: green, B: blue, I: indigo, V: violet"
3. It should accept an array containing the colors as an argument
4. Run learn locally until you pass
5. Submit the lab

colors will be passed in as: ['red', 'orange', 'yellow', 'green', 'blue', 'indigo', 'violet']

You must read from the colors argument and you can hardcode the order, there is no need to use #each or any loop. For example, given letters = ["b","a","c"] to print them in alphabetical order without iteration you could:

letters = ["b","a","c"]
puts "The first letter in the alphabet is: #{letters[1]}"
puts "The second letter in the alphabet is: #{letters[0]}"
puts "The third letter in the alphabet is: #{letters[2]}"