The problem with D's properties

[Mike Franklin]

On Thursday, 31 May 2018 at 01:49:42 UTC, DigitalDesigns wrote:
> https://dpaste.dzfl.pl/6c6e614b58ac
>
> The problem given in the list, is that a ref getter is used 
> when a setter does not exist. Why have a setter then?
>
> One problem is that if the setter has different behavior than 
> the getter there will be problems.
>
> The other problem is that += modifies the value.
>
> normally getters are thought to be immutable in the since that 
> they just return a value.
>
> but
>
> a += will modify what a points to.
>
> Using setters, we might want to trigger an event when the value 
> changes. But since the getter is used and can modify the event 
> won't be triggered.
>
> This is a bad design.
>
> any modifying operator should call the setter. This is 
> precisely what "set mean".
>
>
> a += b is suppose to be syntactic sugar for a = a + b, yet we 
> get different behavior. In one case only a getter is called and 
> in the second case the getter and then the setter.
>
> How D currently handles this is wrong and error prone. Either 
> depreciate the use of op assignments using properties or fix 
> it! lvalues should ALWAYS use the setter, it makes no sense 
> otherwise.

In case you're not already aware, there is a DIP in progress to 
remedy this issue:  https://github.com/dlang/DIPs/pull/97.  A few 
bugs have already been filed on this, and the DIP intends to 
address that.  If you have anything to add, please voice your 
thoughts in the DIP's PR.

Mike