Boolean and nil

true and false are the two values of the class Boolean, and nil, the absence of a value, is the one value of NilClass.

Truthiness

Only false and nil count as false in a condition. Everything else is true, 0, "" and [] included.

puts(0 ? "true" : "false")      # true
puts("" ? "true" : "false")     # true
puts(nil ? "true" : "false")    # false
puts(nil || 5)                  # 5

!, && and || work on any values, && and || giving one of their operands; see Operators. &, | and ^ aren’t defined for Booleans.

Boolean

to_s

b.to_s
b.inspect

"true" or "false". Returns: String.

to_i

b.to_i
b.to_f

1 for true, 0 for false: for counting what holds. Returns: Number.

invert

b.invert

The other Boolean, as !b. Returns: Boolean.

holes = [true, false, true]
puts holes.map { |h| h.to_i }.sum   # 2
puts true.invert                    # false

nil

nil answers only the methods every value has (Object): nil.nil? and nil.empty? are true, nil.inspect is "nil" and nil.class is NilClass. It has no to_s, to_a or to_i.

puts nil prints nil, and so does "#{nil}", where Ruby gives an empty string. Test for it first, or give a default with ||: "#{label || ""}".

Passing nil for an optional parameter of a built-in leaves the parameter unset, as if it weren’t given: slice(nil) and segments: nil take their defaults. A method of your own does the same for a parameter with a default (see Methods), so a value passed on may be absent.

label = nil
puts label.nil?                     # true
puts "[#{label || "unnamed"}]"      # [unnamed]