Chapter 4

Question 1

What is a helper?

Answer 1

A user-defined function in Rails

Question 2

Where are files for helpers stored?

Answer 2

app/helpers

Question 3

T/F: Each helper file corresponds to an ERB layout, and provides its functions to it.

Answer 3

T

Question 4

What is the command to start the rails console?

Answer 4

$rails console

Question 5

How are ‘puts’ and ‘gets’ pronounced? Why?

Answer 5

as “put ess” and “get ess”, short for put string and get string.

Question 6

T/F: The ‘print’ function appends a newline character.

Answer 6

F; only ‘puts’ does this

Question 7

T/F: Single-quote strings support interpolation and escape characters.

Answer 7

F; only double quoted strings allow for interpolation and escape characters; single-quoted strings print all characters as their literal values.

Question 8

How can we guarantee we never have to deal with the error produced by the following code:

nil.empty?

Answer 8

always change it to a string:

nil.to_s.empty?

returns true

Question 9

What are the ONLY two ruby objects which return false when used as a boolean?

Answer 9

‘false’ and ‘nil’

Question 10

How are ‘if’ and ‘unless’ statements related?

Answer 10

Both can be placed after a statement to determine if the preceding statement is executed by evaluating the proceeding statement

Question 11

What is the point of the ‘!!’ operator?

Answer 11

Used as a unary operator it converts any object to a boolean value

Question 12

How does the ruby interpreter know whether to read an if statement as the beginning of an if-else block or a condition at the end of a statement?

Answer 12

When used in the same manner as ‘unless’, if statements do not include an ‘end’ keyword

Question 13

What is the point of the ‘module’ keyword?

Answer 13

It allows classes to use the modules with the ‘include’ keyword

Question 14

T/F: Ruby arrays can contain more than one type.

Answer 14

T

Question 15

How can a range be converted to an array?

Answer 15

(0..9).to_a

Question 16

What does the following code do:

a = %w[foo bar baz quux]

Answer 16

Creates an array of 3 strings

Question 17

T/F: Ranges work with letters and numbers.

Answer 17

T

Question 18

What is the equivalent of the following code:

%w[A B C].map(&:downcase)

Answer 18

%w[A B C].map{|c| c.downcase}

Question 19

What does the following code return:

(‘a’..’z’).to_a.shuffle[0..7].join

Answer 19

7 random letters

Question 20

What is the following code shorthand for:

h1 = { name: “Michael Hartl”, email: “michael@example.com” }

Answer 20

h1 = { :name => “Michael Hartl”, :email => “michael@example.com” }

Question 21

What needs to be passed to a block when a hash uses a method requiring a block?

Answer 21

|key, value|

Question 22

What does the ‘inspect’ method do?

Answer 22

Returns the literal value of an object

> > puts “It worked!”, “It worked!”.inspect
It worked!
“It worked!”

> > puts :name, :name.inspect
name
:name

Question 23

What is the ‘p’ function shorthand for?

Answer 23

puts object.inspect

Question 24

Can symbols include ‘-‘ characters?

Answer 24

No

Question 25

T/F: Curly braces are always required when defining hashes.

Answer 25

F; they can be omitted if the hash is the LAST argument in a function call, because the interpreter will know to add all excess arguments to the hash.

Question 26

Why is ‘h = Hash.new’ different from ‘h = Hash.new(0)’

Answer 26

The latter means that any query to a nonexistent key will return the default value given as the constructor argument.

Question 27

What is the difference between an instance method and a class method?

Answer 27

Class methods are called on the class itself, instance methods are called on individual instances.

Question 28

Can the ‘superclass’ method be chained?

Answer 28

Yes, in fact it HAS to be chained:

> > s.class.superclass.superclass

Question 29

Say we have a class that takes a string as an argument to all of its methods: what is a smart alternative to defining an entirely new class?

Answer 29

Either extend the String class or make your new class inherit from the String class

Question 30

If no inheritance is defined when defining a new class, what will the class inherit from?

Answer 30

The ‘Object’ class, which inherits from ‘BasicObject’.

This effectively means that ALL Ruby objects inherit from ‘BasicObject’

Question 31

What is the ‘self’ keyword for?

Answer 31

To specify the object itself.

Question 32

What does the rails method ‘blank?’ do, and how is it different from ‘empty?’

Answer 32

‘blank?’ returns true if the string is empty OR consists of only whitespace; ‘empty’ returns false if consisting of only whitespace

Question 33

In Ruby require statements, why is the ‘./’ necessary for the current directory?

Answer 33

’.’ is Unix for the current directory