[phobos] The @property experiment

[Jonathan M Davis]

On 2011-04-08 13:42, Michel Fortin wrote:
> I made an experiment last month: I changed an "#if 0" to "#if 1" in the
> compiler source, one that was meant to enable proper enforcement of the
> property syntax. Then I went on an fixed a things everywhere to make
> everything compile and work.
> 
> It turned out to be a colossal task to fix everything that needed fixing (a
> few things DMD but most problems coming from Phobos and Druntime), and
> after doing a lot of it I started working on other things and left the
> project untouched since then.
> 
> I'd have preferred to present something finished, but given that I'm not
> sure when I'll work on it again I though it might be a good idea to let
> someone else take over (if someone wants to). Even if no one works on it,
> it might be interesting as a way to see how many things have been relying
> on the non-enforcement of @property. You can look at the "@property"
> branch in my dmd, druntime and Phobos forks on github to see what was
> affected by this change:
> 
> DMD:
> <https://github.com/michelf/dmd/commits/%40property>
> 
> Druntime:
> <https://github.com/michelf/druntime/commits/%40property>
> 
> Phobos:
> <https://github.com/michelf/phobos/commits/%40property>
> 
> Status: Druntime changes should be complete, Phobos is incomplete and I
> think I was stuck on a compiler bug triggered by it when I stopped working
> on it last month, so there might be still a few things to fix in the
> compiler.

I don't know what dmd fixes you did, but I believe there are several bugs 
relating to @property which make it so that some things with properties would 
become impossible. One issue which is going to require either a change in dmd 
or Phobos is http://d.puremagic.com/issues/show_bug.cgi?id=5707 . There are 
several functions in std.file which make perfect sense as properties when they 
take strings but don't make as much sense as properties when they take an int 
(and _can't_ be properties without UFCS). Functions such as isFile and isDir 
either take a string which holds a path or a uint which holds the attributes 
of a file. The compiler currently enforces that a property function is a 
property function for all of its overloads and that doesn't work in this case. 
I don't know why that restriction is in place (possibly because the compiler 
deals with property syntax _before overload resolution?), but it's a problem 
for std.file which makes it so that either those functions can't be 
properties, the attribute version must be renamed, or dmd has to be fixed.

I also recall there being a bug which required property functions which 
returned a ref to be called with parens in at least some cases, though I don't 
know what bug # it would be.

So, there are definitely some changes that need to be made in dmd before 
@property can be enforced, even if Phobos or druntime used them correctly 
(which it can't in some cases). So, if you fixed them, that's great. If not, 
whoever keeps on with the work still has quite a bit of work to do.

Regardless, the fact that we use properties as much as we do in Phobos should 
definitely help in making sure dmd works correctly with @property.

- Jonathan M Davis