w1d2

Question 1

What are 4 basic style tenets?

Answer 1

◦Indent your code.
◦Limit lines to 72 chars.
◦Avoid long methods and nesting more than two levels deep.
◦Don’t over-comment.

Question 2

What is a good rule of thumb regarding DRY?

Answer 2

A good rule of thumb with DRY is that if you find yourself copying and pasting code into other places, you should most likely refactor to avoid duplication.

Question 3

Explain what the =~ operator does.

Answer 3

Returns the first position in the (left-hand operator) string that matches the regex (right-hand operator)

Question 4

Explain the ‘||’ trick.

Answer 4

Can be used to return the value on the right-hand side of the operator if the left-hand side evaluates to nil.

Question 5

What is the recommended maximum number of lines for methods?

Answer 5

10

Question 6

What property do the best methods have?

Answer 6

They are “atomic”; they do an single thing/have a single responsibility

Question 7

What does making atomic methods and giving them logical & descriptive names do?

Answer 7

Makes our code (specifically our main function) EXTREMELY readable, to the point that anyone can read it like plain English to understand what it does. To see the specific implementation of a method, they can see the definition of that method.

Question 8

T/F: Methods should not modify global variables, nor should they attempt to access values other than those given to them as arguments.

Answer 8

T

Question 9

What is the best practice when writing a function to modify its given arguments?

Answer 9

They should only change the arguments if that is the EXPLICIT purpose of the method; otherwise, create a copy of the argument.

Question 10

When should you use the following naming styles:

snake_case
CamelCase
SCREAMING_SNAKE_CASE
question_mark?
bang!

Answer 10

• Use snake_case (not CamelCase ) when naming methods, variables, and files.
• Use CamelCase for classes and modules.
• Use SCREAMING_SNAKE_CASE for other constants.
• Methods that return a boolean value (i.e. true or false ) should end with a question mark (e.g., Array#empty? ).
• Methods that are potentially ‘dangerous’ (e.g., because they modify the calling object or arguments) should end with an exclamation mark (e.g., Array#map! changes the original array).

Question 11

Name a few guidelines for choosing variable names.

Answer 11

Make names as long as necessary, but as short as possible.

For methods that have no side-effects and just return a value, try using a description of the return value (‘cosine’, ‘square_root’)

For methods that do have side-effects, try using a verb followed by a noun(‘print_cosine’, ‘record_square_root’)

Establish conventions for common operations (‘get_cosine’, ‘set_square_root’)

Question 12

Say we have a set of objects that hold data of the the same types. What is an elegant solution?

Answer 12

Make an array of hashes with matching keys:

cats = [{
  :name => "Breakfast",
  :age => 8,
  :home_city => "San Francisco"
}, {
  :name => "Earl",
  :age => 2,
  :home_city => "San Francisco"
}]

Question 13

What is a rule of thumb for using hashes?

Answer 13

Use a hash to collect variables that go together.

Question 14

What is an instance?

Answer 14

An occurrence of an object.

Question 15

What is a class?

Answer 15

A structure that combines state (data, fields) and behavior (methods).

Question 16

T/F: Class names are capitalized and snake_cased.

Answer 16

F; Class names are capitalized and CamelCased.

Question 17

Y/N: It is good for the ‘initialize’ method to perform actions in addition to setting data.

Answer 17

N; initialize should only handle data by setting up an object; logic can be put into a ‘run’ method.

Question 18

What is an instance method and how do we call it?

Answer 18

A method defined on an instance of a class, called as instanceName.methodName

Question 19

When should we use attr_reader over attr_accessor

Answer 19

When we want to prevent the user from changing an instance variable but still be able to see it.

Question 20

T/F: class methods cannot access class variables.

Answer 20

T; there is no instance they even have access to.

Question 21

What is a “factory method”?

Answer 21

A class method which creates a new object.

Question 22

What is the syntax for notating instance methods vs. class methods?

Answer 22

ClassName#instance_method

ClassName::class_method

Question 23

When might we want to define a class method?

Answer 23

When we want a factory method, or when we want a method doesn’t rely on instance data.

Question 24

Y/N: Can we omit the ‘self’ when calling instance/class methods from within the object?

Answer 24

Y; Ruby will add the ‘self’ automatically, and this is the preferred style.

Question 25

What is the difference between Kernel#puts and Kernel#print ?

Answer 25

‘puts’ appends the newline character, ‘print’ does not.

Question 26

T/F: Kernel#puts appends a newline after each element in an array.

Answer 26

T

Question 27

What are the differences between all of the File class methods:

File::open
File::foreach
File::read
File::readlines
File::new

Answer 27

‘open’ opens a file and takes a block. The block can then use File#gets.chomp to get the FIRST line of the file.

‘foreach’ takes a block and does something once per line

‘read’ returns the contents of a file as one long string

‘readlines’ returns each line as an array of strings, with each element containing a newline at the end.

‘new’ creates a new file, which can then be used with the methods from ‘Enumerable’:

f = File.new(“todos”)
f.each {|line| puts “#{f.lineno}: #{line}” }

Question 28

How do we open a file in append mode, and how doe we open a file in write mode? What is the difference?

Answer 28

File.open(“filename”, “a”)
File.open(“filename”, “w”)

Note that each of these takes a block, and then uses that block to put things into the file (can use File#puts for this purpose)

Write mode will delete the existing contents of the file, whereas append mode will not.

Question 29

What is the method to close a file?

Answer 29

File#close

Question 30

T/F: $stdin and $stdout are just File objects.

Answer 30

T; this is why they share gets and puts methods, b/c the Kernel is actually calling these as instance methods from the two constants.

Question 31

How do we access command line arguments from within a script?

Answer 31

the ARGV array of strings.

Question 32

When should a while loop be used.

Answer 32

When we want to repeat an action until something happens, but we don’t know when that something will happen.

Question 33

What is the keyword to break out of a loop?

Answer 33

‘break’

Question 34

What is Enumerator#each_with_index , and how do we use it?

Answer 34

It is an each method that automatically keeps track of the index:

my_favorite_number = 42
numbers = [42, 3, 42, 5]

favorite_indices = []
numbers.each_with_index do |number, index|
  if number == my_favorite_number
    favorite_indices << index
  end
end

Question 35

Y/N: Can we use Enumerator#each with ranges?

Answer 35

Y

Question 36

What is one smart way to use an explicit return to exit a function early if a certain condition is met?

Answer 36

Use ‘unless’:

def go_home
  return unless can_go_home? && wants_to_go_home?

pack_bags
get_tickets
board_plane
end

Question 37

Are return values always meaningful?

Answer 37

Not always; sometimes we just want a method for its side-effects.

Question 38

Why does the || trick work?

Answer 38

Short-circuiting

Question 39

What is the following shorthand for:

@values[n] ||= calculate_fib(n)

Answer 39

@values[n] = @values[n] || calculate_fib(n)

Question 40

T/F: Ruby is a “pass by reference” language.

Answer 40

T

Question 41

What are symbols used for?

Answer 41

To represent the names of things; they are NOT intended for input/output. Used when representing data not meant for I/O

Question 42

Where are options hashes declared, and how are they declared?

Answer 42

They must be the LAST argument, and are declared as options = {}