Comparison Operators
Bean Cart gives a loyalty stamp when an order is at least 5.00. The check total >= 5 looks trivial, but Ruby has several ideas of "equal", and one surprising operator, <=>, that powers every sort you will ever run.
The rule
==compares values,equal?compares identity,<=>answers minus one, zero or one.
The everyday operators all return true or false:
total = 5.0
total == 5 # => true (equal value; 5 and 5.0 count as equal)
total != 4.5 # => true (not equal)
total > 4.5 # => true
total >= 5 # => true
"tea" < "tub" # => true (strings compare letter by letter)Strings compare character by character by their character codes, and every capital letter comes before every lowercase one, so "Zebra" < "apple" is true.
For stricter questions, Ruby offers methods:
1 == 1.0 # => true same value
1.eql?(1.0) # => false same value AND same type? No
a = "latte"
b = "latte"
a == b # => true same content
a.equal?(b) # => false not the very same object
a.equal?(a) # => trueThe spaceship operator <=> compares two values and returns -1 if the left is smaller, 0 if they are equal, and 1 if the left is bigger. It returns nil when the two cannot be compared:
4.5 <=> 5.0 # => -1
5 <=> 5 # => 0
"mocha" <=> "latte" # => 1
5 <=> "five" # => nilSorting uses <=> behind the scenes. If you define <=> in your own class, Ruby can sort your objects.
There is also ===, the case-equality operator. It reads best as "does the right side belong to the left?": Integer === 5 is true and (1..10) === 7 is true. You rarely write it yourself, but case statements use it, as you will see later.
The shortcut
Pick the question, then the tool: "same value?" use ==. "same value and same type?" use eql?. "literally the same object?" use equal?. "which comes first?" use <=>.
The question
Does the order total of 5.0 reach the stamp threshold of 5?
Drills
Answer fast — trust the rule.
What does 5 == 5.0 return?
What does 5.eql?(5.0) return?
What does "mocha" <=> "latte" return?
What does 3 <=> "three" return?
With a = "tea" and b = "tea" on separate lines, which is false?
Remember
==compares values,equal?compares identity,eql?adds a type check.<=>answers -1, 0 or 1 (or nil), and sorting depends on it.- Trap: capitals sort before lowercase, and
1 == 1.0is true while1.eql?(1.0)is false.