http://d.puremagic.com/issues/show_bug.cgi?id=3511

           Summary: ref return property confused with property setter
           Product: D
           Version: 2.036
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: k-foley@onu.edu


--- Comment #0 from Kyle Foley <k-foley@onu.edu> 2009-11-14 12:56:09 PST ---
import std.stdio;

struct A
{
    private int _prop = 42;

    ref int property() { return _prop; }
    //void property(in int rhs) { _prop = rhs; }
}

int main(string[] args)
{
    A a;

    writeln( a.property );

    a.property = 23; // produces the error below
    /*
    Error: function refProperty.A.property () is not callable using
           argument types (int)
    Error: expected 0 arguments, not 1 for non-variadic function type
           ref int()
    */

    writeln( a.property );

    return 0;
}

---

I think this is a bug, but it may actually be a "feature".

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Witold Baryluk <baryluk@smp.if.uj.edu.pl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |baryluk@smp.if.uj.edu.pl


--- Comment #1 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2010-02-05 05:46:48 PST ---
Yes, this is interesting "feature" but I think it should be marked to be so, be some kind of attributed:


struct A {
    private int x_ = 42;

    @property
    @ref_getter_as_setter
    ref int x() { return x_; }
}

It still can be allowed without this properties, but then compile should emit warning.

What do you think?

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--- Comment #2 from Kyle Foley <k-foley@onu.edu> 2010-02-05 14:30:22 PST ---
(In reply to comment #1)
> Yes, this is interesting "feature" but I think it should be marked to be so, be some kind of attributed:
> 
> 
> struct A {
>     private int x_ = 42;
> 
>     @property
>     @ref_getter_as_setter
>     ref int x() { return x_; }
> }
> 
> It still can be allowed without this properties, but then compile should emit warning.
> 
> What do you think?

I think that properties in general suck.  The only thing I want is the syntax for omitting the parentheses when calling a function without arguments.  I don't want the compiler transforming something like "a.property = 42;" into "a.property(42);".  It seems so bizarre to me, but I must be in the minority.

I would solve this problem by either introducing reference types like C++ or allowing alias this to alias to a dereferenced pointer:

struct Ref(T) {
  T* _ref;
  alias *_ref this;
  this(ref T rhs) { _ref = &rhs; }
}

Then I could implement properties by doing something like this:

struct A
{
    private int _prop = 42;

    PropertyHelper property() { return PropertyHelper(_prop); }
    struct PropertyHelper {
        private int _p;
        private Ref!int _reference;

        alias _p this; // aliased to a copy

        this(ref int rhs)
          : _reference(rhs); // meh, I don't know how to do this in D
        {
            writeln("Log: called the getter");
            _p = rhs; // note this is a copy
        }

        void opAssign(in int rhs)
        {
            writeln("Log: called the setter");
            _reference = rhs;
        }
    }
}

But a problem could be that when doing "auto x = a.property;" the type of x would be PropertyHelper.  I mean, personally I would just do int getProperty(); and void setProperty(int); and be done with it.

Anyways, I think we need to provide more general functionality from the compiler so that cool things can be done with libraries (e.g. letting alias this do more like the example above).

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED


--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2011-06-22 00:16:11 PDT ---
https://github.com/D-Programming-Language/dmd/commit/3d5f405babe65f65ebd2e1c92e9b84ee30eaee8d

https://github.com/D-Programming-Language/dmd/commit/84e95255e51d02512935560de3424410ace1ba67

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