Properties: a.b.c = 3

[KennyTM~]

Bill Baxter wrote:
> On Wed, Jul 29, 2009 at 9:23 AM, Jarrett
> Billingsley<jarrett.billingsley at gmail.com> wrote:
>> On Wed, Jul 29, 2009 at 10:44 AM, Ary Borenszweig<ary at esperanto.org.ar> wrote:
>>> Andrei Alexandrescu wrote:
>>>> Kagamin wrote:
>>>>> Andrei Alexandrescu Wrote:
>>>>>
>>>>>> Kagamin wrote:
>>>>>>> Andrei Alexandrescu Wrote:
>>>>>>>> The question is very simple: given that we're used with a
>>>>>>>> specific semantics for a.b.c = 3, how can we address the fact
>>>>>>>> that the semantics of this familiar operation is so different
>>>>>>>> (and likely so useless) when properties replace fields?
>>>>>>> You're solving problems that never came to life. Well... only as
>>>>>>> syntetic examples.
>>>>>> IMHO it's quite the contrary, a.b.c = 3 is a very simple and
>>>>>> concrete problem that emphatically shows we haven't gotten
>>>>>> properties up to snuff.
>>>>> Never saw this problem in C#.
>>>> Of course you didn't. This is because C# doesn't have it - their structs
>>>> can't define properties.
>>>>
>>>> Andrei
>>> Yes they can. And also C# shows us the solution to the problem (similar to
>>> what Walter proposed).
>>>
>>> ---
>>> public class Bar
>>> {
>>>    public Foo Foo { get; set; }
>>> }
>>>
>>> public struct Foo
>>> {
>>>    public int Property { get; set; }
>>> }
>>>
>>> Bar bar = new Bar();
>>> Foo foo = new Foo();
>>> foo.Property = 10;
>>> bar.Foo = foo;
>>>
>>> bar.Foo.Property = 20; // line 16
>>> ---
>>>
>>> Error on line 16: Cannot modify the return value of 'Bar.Foo' because it is
>>> not a variable
>> Booom, exactly what I said about rvalues.
>>
> 
> Yeh, I don't understand how any of this has anything to do with
> properties.  It's the same question if you ask what should
> 
>  a.b().c = 5
> 
>  do.  It's the same issue whether you have properties or not, and
> needs a solution whether you have properties or not.
> 
> --bb

Probably Walter means

a.b.c = 3;	// b is a field

works, while

a.b.c = 3;	// b is a getter

is a useless call. Nevertheless, if b() uses ref-return then it is 
meaningful.