classes

# A class is a reference: two names can point at one object.

class Counter
  # `property` makes a field readable and writable from outside.
  property count : Int32

  def initialize(@count : Int32)
  end

  def bump : Nil
    @count += 1
  end
end

a = Counter.new(0)
b = a          # b is the same counter, not a copy
b.bump
b.bump
puts a.count   # 2: the change is visible through a

# A struct behaves differently: `b = a` would copy, and `a` stays at 0.
# Use a struct for small values, a class for things that have identity.
struct Cell
  property value : Int32

  def initialize(@value : Int32)
  end
end

x = Cell.new(0)
y = x
y.value = 5
puts x.value   # 0