Is it possible to store properties via opDispatch using tuples?

[Gary Willoughby]

On Friday, 17 January 2014 at 17:50:54 UTC, H. S. Teoh wrote:
> On Fri, Jan 17, 2014 at 05:29:14PM +0000, Gary Willoughby wrote:
>> On Friday, 17 January 2014 at 15:56:46 UTC, H. S. Teoh wrote:
>> >Couldn't you just return a Variant? I thought this is what 
>> >Variants
>> >are made for.
>> >
>> >
>> >T
>> 
>> Yes but then i would need to coerce it to get it's underlying 
>> type.
>
> But isn't that what you'd have to do anyway? I mean, how else 
> would the
> following code work?
>
> 	class DynClass {
> 		...
> 		auto opDispatch(string field)() {
> 			return dotDotDotMagic();
> 		}
> 	}
>
> 	void main(string[] args) {
> 		auto d = new DynClass();
> 		if (args[1] == "int")
> 			d.abc = 123; // d.abc = int
> 		else
> 			d.abc = "xyz"; // d.abc = string
>
> 		// Suppose this somehow works:
> 		auto x = d.abc;	// what's the type of x?
> 	}
>
> Since the type of x must be known at compile-time, but the type 
> of d.abc
> can't be known until runtime, the above code can't possibly 
> work unless
> d.abc returns a Variant. It's simply not possible for a
> runtime-determined type to be put into a variable of 
> compile-time
> determined type without some kind of runtime check.
>
> Now I'm not sure if Variant allows assignment to a static type, 
> but in
> theory this should be possible:
>
> 	// assume d.abc returns a Variant
> 	int x = d.abc; // will assert if d.abc doesn't hold an int at 
> runtime
>
>
> T

In the example in my original post the types are known at compile 
time but they are different between properties. I wondered if 
there was a solution to storing and retrieving while preserving 
the original type via opDispatch.

I have a working solution but it only stores the base type. So i 
f i have an inheritance chain like this:

A -> B -> C

I can store properties of type A, B and C but when i retrieve 
them they all come back as A because of array covariance. I 
wonder if there is a way of casting them automagically to the 
correct type.