[swift-users] strange property observer behavior

[adelzhang at qq.com]

Hi,

The following code works fine. The property `a` is stored twice. But
it don't enter infinite loop.

     class Foo {
         var a: Int = 0 {
              didSet {
                  a = a + 1
              }
         }
     }

     let foo = Foo()
     foo.a = 2
     print(foo.a) // output 3


Regards

--adel


在 Mon, 05 Sep 2016 00:27:16 +0800，Gerard Iglesias  
<gerard_iglesias at me.com> 写道:

> Hi,
>
> didSet is called as soon as the property is stored… Excepted when the  
> value is stored in the initialiser code.
>
> For me it is completely predictable that your code enter an infinite loop
>
> Regards
>
>
>> On 4 Sep 2016, at 17:11, adelzhang via swift-users  
>> <swift-users at swift.org> wrote:
>>
>> Thanks for reply.
>>
>> How does Swift choose *rules* as you said?
>>
>> Swfit encourage to override the property observer. But when we change  
>> the own property in Child class's `didSet` observer, that would cause  
>> infinite loop:
>>
>>     class Base {
>>         var a: Int = 0
>>     }
>>
>>     class Child : Base {
>>         override var a: Int {
>>             didSet {
>>                  a = a + 1
>>             }
>>         }
>>      }
>>
>>      let child = Child()
>>      child.a = 3
>>
>> Any differcen with situation 1?
>>
>>