takeUntil

import std.algorithm;
import rx;

auto source = new SubjectObject!int;
auto stopper = new SubjectObject!int;

int[] buf;
auto disposable = source.takeUntil(stopper).doSubscribe!((n) { buf ~= n; });

source.put(0);
source.put(1);
source.put(2);

stopper.put(0);

source.put(3);
source.put(4);

assert(equal(buf, [0, 1, 2]));