This document discusses ways that Ruby code can be "weird" compared to other languages. It covers 11 weirdnesses: 1. Parallel variable assignment 2. Method names ending with ? for booleans 3. Everything having a boolean value 4. if/unless statements returning values 5. The unless keyword for negative conditions 6. Iterators like loop and times for loops 7. Iterators for arrays and strings 8. Optional parentheses for method calls 9. Methods being able to take blocks 10. Implicit return of the last expression in a method 11. Resources for learning more about Ruby idioms

1. How To Be Weird
The Idiomatic Ruby Ways

2. https://www.youtube.com/watch?v=5MgBikgcWnY
It takes 20 hours of deliberate practice to be reasonably good at something, anything.

3. The Algorithm of
Rapid Ruby Acquisition
1. Learn enough to self-correct
2. Practice at least 20 hours

4. Practice at least 20 hours
codeeval.com
The second step is easy. There are numerous online resources for you to practice. One example of them is codeeval.com

5. Learn enough to self-correct
listen to this talk
The first step, however, is easier. You only have to listen to this talk.
That’s recursion right there

6. Learn enough to self-correct
• Assignment
• Naming
• Control Expressions
• Methods

7. Assignment

8. Weirdness #1
Parallel Assignment

9. a = 'foo'
b = 'bar'
c = 'baz'
d = 'foobar'
Instead of doing this:
You can do:

10. a, b, c, d = 'foo', 'bar', 'baz', 'foobar'
this:
but just because you can doesn’t mean you should: readability is bad

11. a = 'foo'
b = 'bar'
a, b = b, a
good 1: swap variable assignment

12. def multi_return
[1, 2]
end
a, b = multi_return
good 2: multiple return values from a method

13. Naming

14. Weirdness #2
Method names can end with ?s

15. they return a boolean

16. examples
• String#empty?
• String#include?
• String#start_with?
• String#end_with?
• Array#empty?
• Array#include?
• Range#include?
• Object#respond_to?
• Object#nil?
• Object#is_a?
Obejct#is_a? synonymous kind_of?/instance_of?

17. Control Expressions

18. Weirdness #3
everything has a Boolean value
Every expression in Ruby evaluates to an object, and every object has a Boolean value of either true or false? true and false are objects

19. if 0
puts “0 is true”
else
puts “0 is false”
end
what is the output?

20. Only two objects has a false
value, nil and false itself
Every expression in Ruby evaluates to an object, and every object has a Boolean value of either true or false? true and false are objects

21. Weirdness #4
if statements return a value

22. if(condition1) {
result = x;
} else if(condition2) {
result = y;
} else {
result = z;
}
In Java
if condition1:
result = x
elif condition2:
result = y
else:
result = z
In Python

23. In Ruby
if statements return a value

24. The evaluation of the last
executed statement.

25. result =
if condition1
x
elsif condition2
y
else:
z
end
In Ruby

26. Exercise

27. what is the value of result?
result =
if true
puts “hello”
“hello”
else
“world”
end
“hello”

28. what is the value of result?
result =
if false
“hello”
else
“world”
puts “world”
end
nil

29. The evaluation of the last
executed statement.

30. Weirdness #5
the unless keyword

31. if !condition
do_something
end
negative condition unless
unless condition
do_something
end

32. Observation:
Ruby cares about readability

33. so much so that
(Weirdness #6)
Ruby has modifier if/unless
so this is not good enough

34. if !condition
do_something
end
negative condition unless
unless condition
do_something
end
so this is not good enough

35. do_something if !condition
negative condition unless
do_something unless condition
this is
Question: which one is better? Choose unless over if with negative condition

36. Weirdness #7
iterators
iterators help you iterate

37. how to do an infinite loop?
iterators help you iterate

38. while(true) {
doSomething();
if(condition1) {
break;
}
if(condition2) {
continue;
}
}
In Java
while True:
do_something()
if condition1:
break
if condition2:
continue
In Python

39. loop do
do_something
break if condition1
next if condition2
end
In Ruby

40. loop is a method, not a keyword
loop do
do_something
break if condition1
next if condition2
end
Kernel#loop repeatedly executes the block.
We call this kind of ruby methods iterators. They take a block, and execute the block repeatedly.

41. how to do something a certain
number of times?
iterators help you iterate

42. for(int i = 0; i < 10; i++) {
doSomething();
}
In Java
for i in range(10):
do_something()
In Python

43. 10.times do
something
end
In Ruby

44. 10.times do |i|
puts i
end

45. 5.upto(10) do |i|
puts i
end

46. 10.downto(1) do |i|
puts i
end

47. Weirdness #8
iterators - Array and String

48. how to iterate an array?
iterators help you iterate

49. for(int i : a) {
doSomething(i);
}
In Java
for i in a:
do_something(i)
In Python

50. a.each do |i|
do_something(i)
end
In Ruby
demo
also demo each_with_index

51. how to iterate a String?
iterators help you iterate

52. In Java
String s = “hello";
for(int i = 0; i < s.length(); i++) {
System.out.println(s.charAt(i));
}

53. In Python
s = “hello"
for c in s:
print c

54. In Ruby
s = “hello"
s.each_char do |char|
puts char
end
demo
also demo: how to print index of each char

55. Methods

56. Weirdness #9
method calls

57. parenthesis are optional when
calling methods

58. puts “hello” puts(“hello”)
Omit parentheses when:
Omit parentheses around parameters for methods that are part of an internal DSL (e.g. Rake, Rails, RSpec),
methods that have "keyword" status in Ruby (e.g. attr_reader, puts) and attribute access methods. Use parentheses around the arguments of all other method
invocations.

59. omit parentheses when:
• there are no arguments
• the method is part of internal DSL
• the method has “keyword status”
attr_reader, puts, print
Omit parentheses when:
Omit parentheses around parameters for methods that are part of an internal DSL (e.g. Rake, Rails, RSpec),
methods that have "keyword" status in Ruby (e.g. attr_reader, puts) and attribute access methods. Use parentheses around the arguments of all other method
invocations.

60. Weirdness #10
methods can take blocks
a lot of ruby methods take blocks

61. add 1 to every element in an array

62. In Java
int[] a = {1, 2, 3};
for(int i = 0; i < a.length; i++) {
a[i]++;
}

63. In Python
a = [1, 2, 3]
for i in range(len(a)):
a[i] += 1

64. In Ruby
a = [1, 2, 3]
a = a.map { |i| i + 1 }
Demo
Array#collect = Array#map
Invokes the given block once for each element of self.
change every int to string

65. get the sum of all elements in an array

66. In Java
int[] a = {1, 2, 3};
int sum = 0;
for(int i = 0; i < a.length; i++) {
sum += a[i];
}

67. In Python
a = [1, 2, 3]
sum = sum(a)

68. In Ruby
a = [1, 2, 3]
sum = a.inject { |a, e| a + e }
Demo
Enumerable#reduce = Enumerable#inject
shortcut: inject(:+)

69. Rails flavoured Minitest cases

70. class SomeControllerTest < ActionController::TestCase
test “should do stuff” do
assert_equal 2, 1 + 1
end
def test_should_do_stuff
assert_equal 2, 1 + 1
end
end

71. Weirdness #11
implicit return in methods
a lot of ruby methods take blocks

72. the evaluated object of the last
executed expression in a method
is implicitly returned to the caller
Every expression in Ruby evaluates to an object,

73. def greet
puts “hello”
“hello”
end
what is returned?
def greet
“hello”
puts “hello”
end
def greet
return “hello”
puts “hello”
end

74. References:

75. The Well-Grounded Rubyist
by David A. Black

76. Ruby Style Guide
https://github.com/bbatsov/ruby-style-guide

77. Thanks
@ZhifuGe
codingdojo.io