spir wrote:
> Using properties allows travesting a method call into direct data
access. What if the underlying member actually is plain data? Would it
be possible to provide a real data member where the language expects a
property (for instance as range empty & front properties)?
There has been a lot of discussions on properties and their syntax.
There is a complexity in your proposal: should we allow write access to
@property members? We would need to come up with a way to limit write
access.
> Is there any difficulty for the compiler to check whether a data
member of the same name and correct type exists? To help it, we could
mark said data member with an @property hint. For instance:
>
> struct String {
> char[] cs;
> private uint index = 0; // for traversal
> @property char front;
> @property bool empty;
> this (string characters) {
> this.cs = characters.dup;
> this.empty = (this.cs.length == 0);
> if (this.cs.length > 0)
> this.front = this.cs[0];
> }
> @property void popFront () {
> ++ this.index;
> this.empty = (this.index >= this.cs.length);
> if (this.index < this.cs.length)
> this.front = this.cs[this.index];
> }
> }
> unittest {
> auto s = String("abc");
> // works fine
> while (! s.empty) {
> auto c = s.front;
> write(c,' ');
> s.popFront;
> }
> writeln();
> // works not
> //~ foreach (char c ; s) write(c,' ');
> writeln();
> }
>
> Here, popFront does not only advance, it correctly sets empty and
front, so that a single method is needed. But the language expects a
method-property (actually, it complains for missing opApply *).
Phobos is happy with 'empty' being a static member. The following member
would make an infinite range:
static enum bool empty = false;
But I know that you don't want that. :)
The actual problem in your example is the missing front() function.
> I'm a bit troubled to implement methods where plain data does the job
and conceptually better matches my model (maybe it's only me: I wish the
code to mirror my views).
Having never used a language that had properties, I am very happy how D
handles them. Having to write a one-liner doesn't bother me.
Ali
