Is it possible to store properties via opDispatch using tuples?

H. S. Teoh hsteoh at
Fri Jan 17 09:49:22 PST 2014

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") = 123; // = int
		else = "xyz"; // = string

		// Suppose this somehow works:
		auto x =;	// what's the type of x?

Since the type of x must be known at compile-time, but the type of
can't be known until runtime, the above code can't possibly work unless 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 returns a Variant
	int x =; // will assert if doesn't hold an int at runtime


There are 10 kinds of people in the world: those who can count in binary, and those who can't.

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