@property Incorrectly Implemented?

[John via Digitalmars-d]

On Saturday, 17 September 2016 at 10:55:59 UTC, Ethan Watson 
wrote:
> On Friday, 16 September 2016 at 20:52:37 UTC, John wrote:
>> Your comment was out of place, saying properties don't need to 
>> be changed is like saying @property shouldn't even be a D 
>> feature cause you can create the same functional program in 
>> C++, which does not have the property feature.
>
> Stop reading rubbish that isn't there.
>
> And pay attention. MSVC has the __declspec( property ) 
> extension.

MSVC != C++

I'm not going to pay attention to a feature that isn't standard 
and only Microsoft's compiler seems to have.

Since you brought it up though, it's a good chance to look at how 
it behaves.

     struct Test
     {
         int p;
         int& prop()
         {
             return p;
         }

         __declspec(property(get = prop, put = prop)) int& magic;

     };

     void main()
     {
         Test test;

         test.p = 10;

         if(&test.p == &test.magic)
         {
             std::cout << &test.p << '\n' << &test.magic << '\n' 
<< "magic";
         }

     }

I'll give you a hint, it prints magic. Imagine that.

>> You also made a reference to C#, which doesn't even allow you 
>> take address of
>
> And? Properties in C# are a massive example of a comparable 
> feature where executed code is syntactically treated in some 
> ways to a variable.

Yes, you can't take the address of a property in C#, with or 
without unsafe on.

>> So I don't know what you mean by that's how I want to play, 
>> when you instigated said argument.
>
> I indicated you're taking it personally. Which you are.

I wasn't until you indicated that you were taking it personally 
with that statement.

>> It's not really that important. What it allows is returning 
>> references. You can make a comparison to any other language 
>> that has properties it doesn't really matter. This is how D 
>> was implemented. If they wanted to be like every other 
>> language then it shouldn't have been allowed to even return a 
>> reference. But it is does, that's how it's implemented and 
>> odds are it probably won't change now to not allow it. D also 
>> has the "&" implemented, what I am discussing is whether it 
>> was implemented correctly or not. Honestly it is no 
>> implemented correctly. To the point I would actually rather 
>> they remove the functionality so that you can't take the 
>> address of a property. If they are not willing to change it to 
>> function in a different way.
>
> Taking the address of a property and getting a function type is 
> important.
>
> Did you know that this C++ class:
>
> class SomeObject
> {
>   virtual int getSomeValue() const;
>   virtual int setSomeValue( int value );
> };
>
> Matches up exactly to this D class:
>
> extern( C++ ) class SomeObject
> {
>   @property SomeValue() const;
>   @property SomeValue( int value );
> }

You have "get" and "set" in the C++ function, so no it doesn't 
match it exactly. Semantics aside, you shouldn't be referencing 
behavior of properties in a language that doesn't even have 
properties. It's simply a way to emulate properties. If C++ had 
properties, I would imagine they would behave like the above MSVC 
implementation does. Shouldn't be held back by C++ for such a 
reason, you can easily take off those property attributes and 
that would probably be the saner solution. So that it actually 
functions the same, in that you need the use the paranethese to 
set and get the variable. That aside I doubt you ever take the 
pointer of those getters and setters in C++ either.

>> Anyways a bitfield can't actually represent a single, there's 
>> no type for a bit. The smallest type is a byte, which is 8 
>> bits. So even if it wasn't a property there's no way you can 
>> take the address of a bit. So that's the first issue, you are 
>> trying to use an example that doesn't make sense even outside 
>> the concept of properties. The second issue is, this is 
>> defined behavior. You can't take the address of a rvalue, 
>> there's an ideone link in my previous post show this if you 
>> missed it. So taking the address of a property would return an 
>> error if it didn't return a reference.
>
> What you're suggesting, and why I brought up the example, is to 
> change the implementation details of properties for *one* use 
> case. This has wide ranging implications that you've clearly 
> not thought of. Like if I was to take the address of that 
> property for the purposes of exposing a function to C++. You 
> want to make it so I don't get that function? Or that there's 
> some extra convoluted method of getting it solely because you 
> think a property should be something that it's not?

One use case is better than the zero use case it current holds.. 
And using it to identify whether a member is a property is a 
misuse and i'd actually count that as a negative. So negative one 
use case.

>> Well that's how it is currently implemented actually.
>>
>>     struct S
>>     {
>>         @property int prop() { return 0; }
>>     }
>>
>>     writeln(typeof(S.prop).stringof) // prints "int", not 
>> "delegate"
>
> Read further. I have suggested that the property resolution 
> order gets changed so that this ambiguity goes away.
>
>> blah blah blah
>
> Yeah I covered everything else already. Not helping your cause 
> by stating your example that started this topic was *satirical*.

Alright then "blah blah blah" as you try to misdirect from all 
the points that were made that you can't create a counter 
argument for.