Ruby

Question 1

How do you create a non-inclusive range from 0 to 4?

Answer 1

0…5

Question 2

s = “12345”

s.slice(0…2) = ?

Answer 2

“12” (non-inclusive range)

Question 3

How do you interpolate variables in a string?

Answer 3

”#{var}asdf”

Question 4

What is this operator called?

”#{thisguy}”

Answer 4

string interpolation operator

Question 5

What are the (2,3,4,5,more?) string case manipulation operators?

Answer 5

upcase, downcase, capitalize, swapcase

Question 6

What are two ways to capitalize a string?

Answer 6

upcase, capitalize

Question 7

How do you lowercase a string?

Answer 7

downcase

Question 8

How do you reverse the cases of a string?

Answer 8

swapcase

Question 9

s = “asdf”

What’s another way to write s.slice(0..1)?

Answer 9

s[0..1]

Question 10

s = “asdf”

What’s another way to write s[0..1] using a method?

Answer 10

s.slice(0..1)

Question 11

a = “asdf”

What will a.delete(‘ds’) return?

Answer 11

“af”

Question 12

a = “asdf”

Using the delete method on a, how can you return “af” ?

Answer 12

a.delete(‘sd’) or a.delete(‘ds’)

Question 13

With two strings, how can you tell which operator will tell you which one comes first alphabetically?

Answer 13

str1 < str2

Question 14

What’s this operator called <=> ?

Answer 14

The spaceship operator

Question 15

What’s the spaceship operator (and what does it do?)

Answer 15

<=>

a <=> b returns:

-1 if a < b
0 if a == b
1 if a > b

Question 16

How do you determine the truthiness of a value?

Answer 16

!!value

The first ! returns true/false, the second ! negates this and returns the truthiness.

Question 17

Why would you ever use !!value ?

Answer 17

To determine the truthiness of value

Question 18

What does !!nil return?

Answer 18

false

Question 19

Two ways to tell if a value is odd:

Answer 19

val % 2 == 1

val.odd?

Question 20

Two ways to tell if a value is even:

Answer 20

val % 2 == 0

val.even?

Question 21

What’s the opposite of a while loop?

Answer 21

An until loop

Question 22

“asdf”.each_char do |ch|
true
end

what does this code return?

Answer 22

“asdf”

Question 23

What does an until loop loop until?

Answer 23

Until a truthy condition is met.

Question 24

What does a while loop evaluate to?

Answer 24

nil

Question 25

How would you explicitly return a value from a while loop?

Answer 25

nest the while loop within a function

Question 26

{ |x| asdf }

What do you call this structure?

Answer 26

block

Question 27

receiver.each {|x| asdf}

What does this return?

Answer 27

receiver

Question 28

What iterator is used to access the characters in a string?

Answer 28

each_char

Question 29

What is each_char used for?

Answer 29

To access each character in a string.

Question 30

What type of block should use do/end?

Answer 30

multi-line blocks

Question 31

What syntax should be used for MULTI-line blocks: do/end or {…} ?

Answer 31

do/end

Question 32

What type of block should use {…}

Answer 32

single-line blocks

Question 33

What syntax should be used for SINGLE-line blocks: do/end or {…} ?

Answer 33

{…}

Question 34

When passing a block to a method, is the block inside or outside of the method’s calling parenthesis?

Answer 34

outside

Question 35

When does a method call not require parenthesis?

Answer 35

when it has no arguments

Question 36

How do you call a method named foo with no arguments?

Answer 36

foo

Question 37

How do you write a method named foo that accepts a block?

Answer 37

def foo(&prc)
prc.call
end

Question 38

What does the &prc represent in this code:

def foo(&prc)
prc.call
end

Answer 38

a block to be passed to foo

Question 39

What’s the difference between a block and a proc?

Answer 39

A block is a term that refers to the code you write, which is wrapped in do/end or {…}.

A Proc is a ruby object that contains the code written in a block.

Question 40

How can you pass multiple procs to a method?

Answer 40

procs #2+ can be passed as arguments.

Question 41

What two things does the yield keyword do?

Answer 41

1. When used within a method, it will call Proc.call on a proc passed to a method.

Question 42

[“a”, “b”, “c”].map(&:upcase)

In the above code, what does the &: do?

Answer 42

It calls #to_proc on the upcase function, converting it to a Proc

Question 43

If you’re calling a single method within a block, what’s a syntactic shortcut?

Answer 43

Use “&:” like so:

[“a”, “b”, “c”].map(&:upcase)

Question 44

How do you check to see if a block was passed to a method?

Answer 44

block_given?

Question 45

Where and why would you use “block_given?” ?

Answer 45

block_given? is used within a method that might accept a block.

The purpose is to allow a conditional yield, without causing a LocalJumpError like so:

def run_block
  yield
end

run_block

this will cause a LocalJumpError. to avoid this, we rewrite run_block like so:

def run_block
  yield if block_given?
end

Question 46

How many blocks can you pass to a method?

Answer 46

1

Question 47

What’s the syntax for a switch?

Answer 47

case value
when X
  puts "a"
when Y
  puts "b"
when Z
  puts "c"
else
  puts "d"
end

Question 48

Why can you pass an argument to a proc using === ?

Answer 48

For syntactic purposes surrounding a case statement.

Question 49

What are the 2 differences between a proc and a lambda?

Answer 49

1. A lambda expects to be called with the correct number of arguments.

Question 50

How would you set up a doubler/tripler closure using a multiple_generator closure?

Answer 50

def multiple_generator(m)
  lambda do |n|
    n * m
  end
end

doubler = multiple_generator(2)
tripler = multiple_generator(3)

puts doubler[5]
puts doubler[10]

Question 51

What are 4 ways of calling a proc named my_proc and passing an argument val?

Answer 51

my_proc.call(val)

my_proc.(val)

my_proc[val]

my_proc === val

Question 52

Why use ‘each’ instead of ‘for’ ?

Answer 52

‘for’ uses a single reference for each element it loops through. if we try to generate references within a for construct, all of those references will be assigned to the final element.

Question 53

(0..10) creates a range of numbers [0,1,2,…,10].

How would you create a range of numbers in reverse order?

Answer 53

Integer#downto

i.e. 5.downto(0).to_a will create:

[0,1,2,3,4,5]

Question 54

How do you check to see if all elements in an array match a given condition? Example for all_even?

Answer 54

Array#all?

arr.all? {|n| n.even? }

Question 55

What does Array#all? do?

Answer 55

Enumerator that ANDs the truthyness of each element of an array.

Question 56

What does Array#non? do?

Answer 56

Enumerator that ANDs the falseness of each element of an array.

Question 57

What does Array#any? do?

Answer 57

Enumerator that ORs the truthyness of each element of an array.

Question 58

How would you check to see if at least one element of an array passes a conditional test?

Answer 58

Array#any?

Question 59

How would you check to see if no elements from an array pass a conditional test?

Answer 59

Array#none?

Question 60

How would you find out how many items in an array match a conditional test?

Answer 60

Pass a block to Array#count

Question 61

What happens when you pass a block to Array#count?

Answer 61

You get back the number of items in the array that, when passed to the block, that have a truthy value

Question 62

Given an array, how would you return a second array containing values that pass a conditional test?

Answer 62

Array#select

Question 63

What does Array#select do?

Answer 63

Returns an array of items that, when passed to select’s block, return a truthy value.

Question 64

What’s the opposite of Array#select?

Answer 64

Array#reject

Question 65

What’s the opposite of Array#reject?

Answer 65

Array#select

Question 66

How would you sort an array by custom criteria?

Answer 66

Array#sort_by

Question 67

What’s a synonym for Array#reduce ?

Answer 67

Array#inject

Question 68

What’s a synonym for Array#inject ?

Answer 68

Array#reduce

Question 69

What are 3 ways to call Array#reduce to sum an array?

Answer 69

arr. reduce(:+)
arr. reduce { |acc, x| acc + x }
arr. reduce(0) {|acc, x| acc + x}

Question 70

What method removes trailing whitespace from a string?

Answer 70

String#rstrip

Question 71

How do you declare a hash “hsh” with keys [0,1,2] and values [‘zero’, ‘one’, two’] to it?

Answer 71

hsh = {0=>’zero’, 1=>’one’, 2=>’two’}

Question 72

What is this symbol called, in relation to hashes?

=>

Answer 72

hash rocket

Question 73

What does the hash rocket symbol look like?

Answer 73

=>

Question 74

What does Hash#include? test its argument against?

Answer 74

hash.keys

Question 75

What are three synonym methods that check whether their argument is a key in a hash?

Answer 75

has_key?

key?

include?

Question 76

What method checks to see if a hash has a value?

Answer 76

has_value?

Question 77

Hash.new(‘blah’)

What does this do?

Answer 77

It creates a new, empty hash, and sets the default value of new hash elements to ‘blah’.

Question 78

How do you set the default value of new hash elements to blah?

Answer 78

Hash.new(‘blah’)

Question 79

What’s a good way to set up a counter hash, h ?

Answer 79

h = Hash.new(0)

Question 80

arr.each_with_index {|a, b|}

Which variable is the element and which is the index?

Answer 80

a = element

b = index

Question 81

How would you open a file and do something to each line?

Answer 81

File.foreach(‘filename.txt’) {|line| … }

Question 82

How would you slurp an entire file as one long string?

Answer 82

contents = File.read(‘filename.txt’)

Question 83

How do you guarantee that a file with handle f that you’ve been writing to will be successfully written to disk?

Answer 83

f.close

Question 84

How do you access parameters passed in on the command line? How about the filename?

Answer 84

ARGV (as an array)

ARGV[0] is the filename

Question 85

What does ARGV contain?

Answer 85

ARGV contains the parameters passed in on the command line

Question 86

What happens if you pass a block to Array.new?

Answer 86

each element of the array will be assigned the value returned by the block

Question 87

How would you preinitialize each value of an array to some value?

Answer 87

By passing a block to Array.new

Question 88

What’s the term to describe multiple assignments done in the same line?

Answer 88

destructuring

Question 89

What property of a symbol prevents it from being changed?

Answer 89

immutability

Question 90

What’s the purpose of a symbol

Answer 90

to represent names of things inside the ruby interpreter

Question 91

What class of objects represents things inside the ruby interpreter?

Answer 91

Symbol

Question 92

What’s the syntax to define a hash using symbols for this data:

“blah” 0
“super” 1

Answer 92

{blah: 0, super: 1}

Question 93

When should a Symbol be used instead of a String?

Answer 93

when representing data that won’t be input or output

Question 94

How would you set up a method that took in an options hash and assigned default values to that hash?

Answer 94

def meth(options = {})
  defaults = {name: 'blah', foo: 'bar'}

options = defaults.merge(options)

…
end

Question 95

How do you access an array containing the current call stack?

Answer 95

Kernel#caller

Question 96

What’s a tight way to refer to a class method my_method in MyClass?

Answer 96

MyClass::my_method

Question 97

What does MyClass::my_method refer to?

Answer 97

a class method

Question 98

How do you delete an item in an array arr at index idx?

Answer 98

arr.delete_at(idx)

Question 99

When reading in a bunch of lines from a text file named ‘foo.txt’, “\n” shows up at the end of each line. How do you prevent this?

Answer 99

File.readlines(“foo.txt”

).map(&:chomp)

Question 100

What’s a faster way to see if a value falls within a range? Why?

Answer 100

Range#cover?

Rather than instantiate an object for each value within range, it instantiates only the first and last objects, then uses logic to figure out if a value is included.

Question 101

What does Range#cover? do?

Answer 101

It checks to see if a value falls within a range WITHOUT instantiating more than 2 elements of that range.

Question 102

How do you call a class method from within a class?

Answer 102

Same as outside a class. ClassName.method_name

Question 103

Why are “and” and “or” used for control flow, rather than for logic?

Answer 103

Their precedence is lower than assignment, therefore only the first and/or will be used before the assignment occurs.

Question 104

What’s the value of result after this statement?

result = true and false and true

Answer 104

true

hint: order of operation