schedulerObject

struct MyDisposable
{
    void dispose()
    {
    }
}

struct MyScheduler
{
    MyDisposable schedule(void delegate() op, Duration val)
    {
        return MyDisposable();
    }
}

class MyClassScheduler
{
    Disposable schedule(void delegate() op, Duration val)
    {
        return null;
    }
}

class MyClassDerivedScheduler : Scheduler
{
    Disposable schedule(void delegate() op, Duration val)
    {
        return null;
    }
}

static assert(isScheduler!MyScheduler);
static assert(isScheduler!MyClassScheduler);
static assert(isScheduler!MyClassDerivedScheduler);

auto s1 = MyScheduler();
auto s2 = new MyClassScheduler;
auto s3 = new MyClassDerivedScheduler;

Scheduler t1 = s1.schedulerObject();
Scheduler t2 = s2.schedulerObject();
Scheduler t3 = s3.schedulerObject();

assert(t1 !is null);
assert(t2 !is null);
assert(t3 !is null);
assert(t3 is s3);

struct MyScheduler
{
    Disposable schedule(void delegate() op, Duration dueTime)
    {
        if (dueTime > Duration.zero)
            Thread.sleep(dueTime);

        op();
        return NopDisposable.instance;
    }
}

MyScheduler scheduler;
Scheduler wrapped = scheduler.schedulerObject();
assert(wrapped !is null);