Method Scope Lab

Objectives

Define a method that takes in an argument and pass a variable in as that argument.
Understand that a variable defined inside a method cannot be used outside of that method.

Instructions

Part I: Passing a Variable Into a Method

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

def catch_phrase
  puts phrase
end

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

Let's take a look at the test for this method in spec/catch_phrase_spec.rb:

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

Go ahead and run the test for this method only by typing rspec spec/catch_phrase_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::CatchPhrase:0x007f87b9cf04c0>

This error is occurring because the code inside the #catch_phrase method is trying to use the phrase variable but we defined this variable on line 5 of our test. In other words, this variable is being defined outside of the method. Our method doesn't have access to it! It is out of scope. Let's fix it!

We need to pass phrase into our #catch_phrase as an argument. Let's do it:

Re-define the #catch_phrase method to take in an argument of a phrase.
Change the test in spec/catch_phrase_spec.rb to match the following:

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

Part II: Understanding Method Scope

Open up lib/rescue_princess_peach.rb and take a look at the following method:

def rescue_princess_peach
  status = "rescued"
  puts "Hooray! Mario has rescued Princess Peach."
end

Notice that the body of this method is setting a variable, status equal to a value of "rescued". Do you think we will be able to access this variable outside of the method? Let's find out!

1 . Comment back in the following lines in your lib/rescue_princess_peach.rb file:

rescue_princess_peach
puts status

2 . Run the file with ruby lib/rescue_princess_peach.rb in your terminal. You should see the following:

Hooray! Mario has rescued Princess Peach.
lib/rescue_princess_peach.rb:12:in `<main>': undefined local variable or method `status' for main:Object (NameError)

We are getting a NameError because status is undefined. Wait a minute, you might be wondering. Didn't we define status inside the #rescue_princess_peach method? We did, but variables defined inside a method are not available outside of that method.

Go back and comment out lines 11 and 12 of rescue_princess_peach.rb.

Run the test suite and you'll see that we are passing all of our tests. If you open up the spec/rescue_princess_peach_spec.rb file, you'll see the following test:

require "spec_helper"

describe "#rescue_princess_peach" do
  it "outputs a message and sets a variable, status, that is not available outside of this method" do
    expect{rescue_princess_peach}.to output("Hooray! Mario has rescued Princess Peach.\n").to_stdout 
    expect{puts status}.to raise_error(NameError)
  end 
end

Notice the last expectation of our test: expect{puts status}.to raise_error(NameError). We expect any attempt to use the status variable to be met with a NameError. Our program, outside of the #rescue_princess_peachmethod, just doesn't know what it is.

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Tokuhisa1/method-scope-lab-dumbo-web-071618

Method Scope Lab

Objectives

Instructions

Part I: Passing a Variable Into a Method

Part II: Understanding Method Scope