Learning Ruby: check equality

There are different ways to determine whether two values are the same in Ruby.

Equality operators: == and !=

The equals operator == will return true if the values compared are equal.

string_one = "Cookies"
string_two = "Cookies"

string_one == string_two   #Output: => true
string_one != string_two   #Output: => false

When we compare numbers of different types (float and integer), the equals operator will return true if both have the same numeric value.

7 == 7.0   #Output: => true

eql?

The eql? method checks both the value type and the exact value it holds. So an integer and a float that have the same numeric value will not be equal.

7.eql?(7.0)   #Output: => false

equal?

The equal? method is the strictest form of comparison in Ruby. It checks whether both values are the exact same object in memory.

a = "Cookies"
b = "Cookies"

puts a.object_id #Output: => 47343105968220
puts b.object_id #Output: => 47343105968200

a.equal? b  # Output: => false

Things are a bit different for numbers, because of the way computers store integers in memory. 7 will always point at the same object id, so if we assign the number 7 to two different variables and use the equal? method on those two variables, the result will be true.

a = 7
b = 7

puts a.object_id # Output: => 15
puts b.object_id # Output: => 15

puts a.equal?(b)  # Output: => true

The spaceship operator <=>

Differently from the previous operators / methods, the spaceship operator does not return true or false, but it returns one of three numerical values.

• -1 if the value on the left is less than the value on the right
• 0 if the value on the left is equal to the value on the right
• 1 if the value on the left is greater than the value on the right

7 <=> 8 # Output: => -1
7 <=> 7.0 # Output: => 0
7 <=> 7 # Output: => 0
7 <=> 1 # Output: => 1

This operator is mostly used for sorting functions.