Property discussion wrap-up

[Zach the Mystic]

On Tuesday, 29 January 2013 at 18:54:09 UTC, H. S. Teoh wrote:
> I agree with all of this, except that currently, as things 
> stand, we
> can't actually implement certain kinds of properties as 
> structs, because
> nested structs do not have access to their parent lexical scope:
>
> 	class Rectangle {
> 		float width, height;
>
> 		// Struct implementation of @property
> 		struct AreaProp {
> 			float value() {
> 				// Error: can't access Rectangle.width
> 				// and Rectangle.height
> 				return width*height;
> 			}
> 			alias value this;
> 			...
> 		}
> 		AreaProp area;
> 	}
> 	void main() {
> 		auto r = new Rectangle;
> 		r.width = 2.0;
> 		r.height = 1.5;
> 		writeln(r.area); // in theory, this should work
> 	}
>
> We'd have to move width and height inside the AreaProp struct 
> to make
> this work, but then we're back to square one (you'd need 
> @property to
> implement .area inside AreaProp).
>
>
> T

This can easily be changed, in my opinion. First, have the 
compiler detect whether the struct has any data members of its 
own. If not, disallow "this" property and "new" operator. Now 
"this" is free to use on a parent struct. However, if you later 
added a data member to the struct, it would break code, so no. 
But maybe we could use something like "outer.this" instead.

Thank you for agreeing with most what what Rob T said!