w2 misc

Question 1

How do you cast in Ruby?

Answer 1

CastType(val)

Question 2

What does Array#compact do?

Answer 2

Removes all nils.

Question 3

Where should you put a collection of functions with no corresponding data?

Answer 3

In a module.

Question 4

In a []= method, is the following argument acceptable:

[2, 2]

Answer 4

No; you must call it with Class[[x y]]

Question 5

What can we do if the super version of a function returns something?

Answer 5

We can store it in a variable.

Question 6

How far do exceptions travel when raised?

Answer 6

They travel up the call stack until they are handled. If they are not, the program exits.

Question 7

If a function will be used in a child class but not in the parent class, how should it be declared in the parent class?

Answer 7

It should be declared to raise an error if called in the parent class, then overwritten in the child class with the specific behavior.

Question 8

How can we set up a parent class to access the constants of an inherited class?

Answer 8

Use the following syntax in the parent class, then declare the constant in the child class:

self.class::CONSTANT

Question 9

How do we pass an array of two elements to a block, when we want to access each element separately?

Answer 9

rows_with_cols_arr.each do |dx, dy|

Question 10

How can we use a ternary operator to toggle a value?

Answer 10

(color == :white) ? -1 : 1

Question 11

How can we use the ternary operator to set the value of a variable?

Answer 11

color = (color == ‘white’) ? ‘black’ : ‘white’

Question 12

T/F: You can include more than one module in a class.

Answer 12

T; only multiple inheritance is invalid.

Question 13

What is one way to catch many types of custom errors?

Answer 13

Make one custom error class which all other custom errors inherit from, then rescue the parent custom class (this will catch all inherited exceptions)

Question 14

Explain #each_with_object

Answer 14

each_with_object([]) do |(dx, dy), moves|

‘moves’ it the blank array, and the first block argument is the object that each was called on.

Question 15

Make an 8x8 grid

Answer 15

a = Array.new(8) { Array.new(8) }

Question 16

How do we set the encoding of a ruby file?

Answer 16

Add the following comment to the top of a file:

encoding: utf-8

Question 17

Why is it ok to use the methods of a class inside the definition of another class which requires it?

Answer 17

B/C nothing is run when the class is declared; it is only evaluated. As long as everything has been loaded by the time the methods are called, everything will run fine.

Question 18

T/F: You can give #shift and #pop arguments to remove a certain number of consecutive elements from the front or back, respectively.

Answer 18

T

Question 19

What does Array#index do?

Answer 19

Takes a value as an argument, then returns the first index where that element is located.

Question 20

Explain Array#product

Answer 20

Creates a new two element array for every element in the argument array paired with every element in the calling array.

Question 21

What is the difference between the two examples:

arry. push(elems)
arry. push(*elems)

Answer 21

Assuming arry and elems are both arrays, the first example will push the entire elems array into arry as a single new element, whereas the splat version will push each element separately into arry, effectively concatenating the two arrays.

Question 22

T/F: Array#delete removes only the first occurrence of the argument element.

Answer 22

F; all occurrences of the argument are removed.

Question 23

T/F: You cannot raise an exception and handle it in the same begin-rescue-end block.

Answer 23

F; You can raise an error in the begin block and rescue it in the rescue block. You can even simply ‘raise “an argument”’, and capture it as a StandardError in the rescue block:

def get_bet 
    begin 
       print "Bet (bankroll: $#{bankroll}) > " 
      bet = gets.chomp.to_i 
       raise 'not enough money' unless bet  e
      puts e.message
      retry 
    end