Type or Nil

• ?

• Nil

• A question mark ? after the type in the function declaration is the same as accepting nil as well.

• Int32? is the same as Int32 | ::Nil

def func(number : Int32?)
  puts number
end

func(23)
func(nil)

# func()
# Error: wrong number of arguments for 'func' (given 0, expected 1)

# func(2.3)
# Error: no overload matches 'func' with type Float64

def show(number : Int32)
  puts number
end

show(23)

# show(nil)
# Error: no overload matches 'show' with type Nil

def other(number : Int32 | ::Nil)
  puts number
end

other(23)
other(nil)