Ruby && vs and

For boolean expressions or flow control, both && and and can be used.

The difference between them is the order of precedence. Operator and has lower precedence than = whereas && has higher precedence than operator =.

Consider these two boolean expressions.

puts var_1 = true && false
puts var_2 = true and false

Output:

false
true

Both expressions return false, but var_1 and var_2 will have different values assigned to them.

var_1 = true && false is equivalent to var_1 = (true && false), var_1 is equal to false.

In contrast, var_2 = true and false will be evaluated as (var_2 = true) and false. This means that var_2 will eventually contain the value true.

puts var_1
puts var_2

Output:

false
true

For this reason, never use and with a ternary operator like this.

s = true and 2.even? ? 'even' : 'odd'
puts s

Output:

true

We may expect it prints even, but instead, it returns true.