Does D have class' attributes like C#'s?

[Basile B.]

On Saturday, 16 December 2017 at 21:11:43 UTC, Marc wrote:
> On Saturday, 16 December 2017 at 20:05:15 UTC, Anonymouse wrote:
>> On Saturday, 16 December 2017 at 19:57:30 UTC, Marc wrote:
>>> C# has a quite nice way to store metadata about a property by 
>>> a feature called atributes[1]. For example, I can write 
>>> something like this:
>>>
>>>> class A {
>>>>    [TextSize(256)]
>>>>    string Name { get; set; }
>>>> }
>>>
>>> So using runtime/reflection I can retrieve the TextSize value 
>>> associated to A.name property.
>>>
>>> Does D have something similar?
>>
>> UDAs? User Defined Attributes.
>>
>> https://dlang.org/spec/attribute.html#UserDefinedAttribute
>> http://ddili.org/ders/d.en/uda.html
>>
>> class A {
>>     @TextSize(256)
>>     string name() { /* ... */ }
>> }
>
> I can't "pack" an object, right? In C#, TextSize is a class and 
> 256 is constructor's first argument. In D it's pretty much an 
> array but I guess it's close enough. Thanks!

No, it's either a struct or a class and it's not included in the 
class itself.
You use the __trait(getAttributes) to retrieve the value when 
needed:

```
struct TextSize {int value;}

class A {
     @TextSize(256)
     string name() { return ""; }
}

class B {
     string name() { return ""; }
}

static assert(__traits(classInstanceSize, A) == 
__traits(classInstanceSize, B));
```