isObservable

struct TestObservable
{
    alias ElementType = int;

    Disposable subscribe(T)(T observer)
    {
        static assert(isObserver!(T, int));
        return null;
    }
}

static assert(isObservable!(TestObservable));
static assert(isObservable!(TestObservable, int));
static assert(!isObservable!(TestObservable, Object));

static assert(isObservable!(Observable!int));
static assert(!isObservable!(Observer!int));
static assert(!isObservable!(string));
static assert(!isObservable!(Object));