类的实例变量是如何在Crystal中实现的?

@my_val 是对实例的引用 MyStruct 在堆栈上。检查此示例并注意差异:

struct MyStruct
  property x

  def initialize(@x : Int32)
  end
end

class A
  getter my_val = MyStruct.new(10)
end


# mutates a struct (passed by reference)
def method(a : A)
  a.my_val.x = 20
end

# does not mutate a struct (passed by value)
def method(s : MyStruct)
  s.x = 30
end

a = A.new
p a.my_val.x       #=> 10

a.method(a)
p a.my_val.x       #=> 20

a.method(a.my_val)
p a.my_val.x       #=> 20 (not 30)