Re: [boost] [property] interest in C# like properties for C++?

Subject: Re: [boost] [property] interest in C# like properties for C++?
From: Edward Diener (eldiener_at_[hidden])
Date: 2009-10-22 23:20:50

Stefan Strasser wrote:
> Am Friday 23 October 2009 01:41:57 schrieb Sid Sacek:
>>>>  [ Edward Diener wrote: ]
>>>>  Manipulating a reference property would be done purely through
>>>> accessing the property. Accessing a reference property returns a T & or
>>>> a T const & depending on whether the property is const or not. In the
>>>> case where a T & is returned the reference property is read/write if T
>>>> itself is not const, since you can manipulate T through the reference,
>>>> whereas in the case where T const & is returned ( or where T & is
>>>> returns but T is itself const), the reference property is read only.
>> Who says that's how properties work?  That just happens to be your version
>> of the implementation details.
> 
> I don't understand what a "reference property" is supposed to be. a property 
> getter can return a reference (if it chooses to do so, not in general, since 
> there may not be an underlying data member), but what is a reference 
> property?

In my implementation a "reference property" is a property whose getter 
returns a reference to the type of the property. A reference property 
does not have a setter. The actual backing data for a "reference 
property" can be a value type itself or a reference. The type T of a 
reference property does not need to be copy constructible.

This is as opposed to what most people, and other language 
implementations, posit as a "property", which is generally a value type, 
meaning that a value is returned by the getter and a value is passed to 
the setter, of the particular type. The type T of a value type property 
does need to be copy constructible in order to pass the value back and 
forth.

My own reasons for bifurcating the notion of a "property" between the 
more common value type property and the reference type property is 
because I do no think a clean implementation of the "property" concept 
can be done in C++ which allows either a reference or a value to be 
returned from the same C++ property implementation.

I am sorry I have not posted my own "property" implementation anywhere 
yet, but I am still working on some other "property" issues which are 
important to me ( besides trying like everyone else to make a living as 
a software designer/programmer ).

I originally added my comments  about a "reference" type property 
because a poster in this thread felt that one could not implement this 
without language support and I do not believe that is the case, and 
wanted to explain in general how one could at least theoretically 
implement a "reference property".

In a way I am arguing for the notion that a single implementation of the 
"property" concept, in other words a single template class which 
implements a C++ "property", while desirable from the point of view of 
usability, may not be practical from the point of view of flexibility 
and an end user's needs.