DIP23 draft: Fixing properties redux

[Dmitry Olshansky]

On 02/05/2013 02:28 AM, Andrei Alexandrescu wrote:> On 2/4/13 2:04 PM, 
Jonathan M Davis wrote:
 >> We could save a lot of boilerplate code if we can simply make it
 >> variables and
 >> property functions guaranteed to be swappable without breaking code.
 >
 > I think this is quite powerful. The way we can do this is by making
 > properties emulate a subset of actual variables.
 >

This is the primary real-world proble to solve.
If tackle it right  we'd secure a sizable flow of Java
converts simply because of this feature alone ;)

More seriously I believe it's worth noting that properties can't emulate 
(in principle) exactly one aspect of variable - taking address
as a pointer. Honestly I can't see a way to overcome it without 
introducing a user-defined way to impose this restriction on a field of 
a struct/class.

Then keeping in mind __traits I have the following clause to add to the 
current proposal:

Inside of aggregate a field marked with @property indicate is 
semantically equivalent to compiler wrapping it with trivial getter and 
setter. Example:
struct Foo{
@property T x;
}

treated  semantically as if:
T __x; // hidden by compiler
//templated to have deduced safe, pure, nothrow
@property T x()()inout{ return x; }
@property void x()(T val){ x = val; }



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Dmitry Olshansky