learn-co-students/programming-univbasics-3-methods-scope-lab-london-web-021720

Method Scope Lab

Learning Goals

• Define a local variable
• Define a method
• Define a method that takes an argument

Introduction

We're going to build a catchphrase generator that output catchphrases from some popular video games. Let's put our knowledge of methods, scope, and variables, to use!

Define a Local Variable

Open up lib/catch_phrases.rb. You should see the following method:

def mario
  status = 'Thank You Mario! But Our Princess Is In Another Castle!'
  puts phrase
end

Note that the method is trying to puts out a variable called phrase.

If we run the test for this method only by typing rspec spec/catch_phrases_spec.rb into your terminal in the directory of this lab. You should see the following error:

NameError:
  undefined local variable or method `phrase' for #<RSpec::ExampleGroups::CatchPhrasesRb:0x007fa5eb399b88>

This error is occurring because the code inside the mario method is trying to use the phrase variable but it's not present inside the scope of the mario method. It is out of scope.

If we look at the test for this method in spec/catch_phrase_spec.rb we can see that it expects "It's-a me, Mario!" to be printed out.

describe "mario" do
  it "puts out 'It's-a me, Mario!'" do
    phrase = "It's-a me, Mario!"
    expect{mario}.to output("It's-a me, Mario!\n").to_stdout
  end
end

We need to define the variable phrase in our mario method. When phrase is called, the output should be "It's-a me, Mario!"

Once phrase is defined in the method, the first test should pass. Let's move on to the next method!

In lib/catch_phrases.rb, take a look at the following method:

def toadstool
  puts status
end

Notice that the body of this method is calling a variable that is set in the mario method. When we run the tests, we are getting a NameError because status is undefined.

Wait a minute, you might be wondering. Didn't we define status inside the mario method? We did, but variables defined inside a method are only accessible to that method. They are not available outside of that method in any other context.

Make sure that the status variable is in the correct context to be used by the toadstool method.

Now that we've walked through a couple of methods, let's define two new methods from scratch!

Define a Method That Outputs a Popular Catch Phrase

Now that our first two tests should be passing, let's try writing a method from scratch on our own. In lib/catch_phrases.rb, define the method link that will output the phrase "It's Dangerous To Go Alone! Take This."

Define a Method That Calls The Other Methods

For our final method, we'll want to define the method all_phrases. This method does not need to take any parameters, but should call the mario, toadstool, and link phrases.

For this method, take a look at our test rspec spec/catch_phrases_spec.rb to see the exact expectation:

describe "all_phrases" do
  it "takes in an argument and puts out the catch phrase" do
    expect{all_phrases}.to output(/It's-a me, Mario!\n/).to_stdout
    expect{all_phrases}.to output(/Thank You Mario! But Our Princess Is In Another Castle!\n/).to_stdout
    expect{all_phrases}.to output(/It's Dangerous To Go Alone! Take This.\n/).to_stdout
  end
end

Now, you could copy and paste the messages from the previous methods, but calling the other methods directly is much easier!

Now run your tests again. If all methods have been written correctly, you should see four tests passing!

Conclusion

We've discussed building methods and recognizing how scope works within the context of each method. With these concepts put together, we can see how it functions in practice. As we discuss scope further, we'll understand more about how to access variables in different scopes.