Choice ranges?

[Artur Skawina]

On 03/28/14 20:00, H. S. Teoh wrote:
> Today I ran into an interesting situation where I have a function f that
> needs to return ranges of different types (but identical element types):
> 
> 	auto f(A...)(A args) {
> 		...
> 		if (someCondition)
> 			return cartesianProduct(x, y)
> 				.joiner;
> 		else
> 			return cartesianProduct(x, y)
> 				.joiner
> 				.filter!someFilter;
> 	}
> 
> This obviously can't compile, because the return types are not the same.
> (Note that someCondition is only known at runtime.) But abstractly
> speaking, it *should* work, because the element type of the returned
> range is identical.
> 
> So how would I implement something like this?

eg
 	auto f(A...)(A args) {
 		...
 		return cartesianProduct(x, y)
 			.joiner
 			.filter!(a=>somecondition?true:somefilter(a));
 	}

artur