Set differences

[bearophile]

Josh:

> Can anyone please explain why this works:
>
> 	auto numbers = sequence!("n")();
> 	auto trimmed = setDifference(setDifference(numbers, 
> sequence!("n * a[0]")(2)), sequence!("n * a[0]")(3));
>
> but this doesn't?
>
> 	auto numbers = sequence!("n")();
> 	auto trimmed = setDifference(numbers, sequence!("n * 
> a[0]")(2));
> 	trimmed = setDifference(trimmed, sequence!("n * a[0]")(3));

This compiles:

void main() {
     import std.stdio, std.algorithm, std.range;

     auto numbers = sequence!("n")();
     auto trimmed = setDifference(numbers, sequence!("n * 
a[0]")(2));
     auto trimmed2 = setDifference(trimmed, sequence!("n * 
a[0]")(3));
     pragma(msg, typeof(trimmed));
     pragma(msg, typeof(trimmed2));
}

Output:

SetDifference!("a < b", Sequence!("n", Tuple!()), Sequence!("n * 
a[0]", Tuple!int))
SetDifference!("a < b", SetDifference!("a < b", Sequence!("n", 
Tuple!()), Sequence!("n * a[0]", Tuple!int)), Sequence!("n * 
a[0]", Tuple!int))


The two trimmed have different type, because in D ranges are 
template-based, so often things have different type, unless they 
are identical.

Bye,
bearophile