with_latest_from itself does not emit current value #374
Description
If you call with_latest_from with the same observable it is called on, the observable passed to with_latest_from does not emit the same value as the observable it has been called on:
#include <iostream>
#include "rxcpp/rx.hpp"
int main()
{
rxcpp::rxsub::subject<int> sub;
auto subscriber = sub.get_subscriber();
auto source = sub.get_observable();
source
.with_latest_from(source)
.subscribe([](auto p) {
// I expect this to be called once,
// but it is not.
std::cout << '[' << std::get<0>(p) << ", " << std::get<1>(p) << "]\n";
});
subscriber.on_next(1);
subscriber.on_completed();
}Expected:
[1, 1]
Got: No output.
If you emit multiple values, the observable passed to with_latest_from still returns the old value (not the same):
#include <iostream>
#include "rxcpp/rx.hpp"
int main()
{
rxcpp::rxsub::subject<int> sub;
auto subscriber = sub.get_subscriber();
auto source = sub.get_observable();
source
.with_latest_from(source)
.subscribe([](auto p) {
std::cout << '[' << std::get<0>(p) << ", " << std::get<1>(p) << "]\n";
});
subscriber.on_next(1);
subscriber.on_next(2);
subscriber.on_next(3);
subscriber.on_completed();
}Expected:
[1, 1]
[2, 2]
[3, 3]
Got:
[2, 1]
[3, 2]
It is the same behaviour if the observable passed depends on the observable with_latest_from is called on:
#include <iostream>
#include "rxcpp/rx.hpp"
int main()
{
rxcpp::rxsub::subject<int> sub;
auto subscriber = sub.get_subscriber();
auto source = sub.get_observable();
auto source_that_depends_on_source = source.filter([](auto x) { return x > 0; });
source
.with_latest_from(source_that_depends_on_source)
.subscribe([](auto p) {
std::cout << '[' << std::get<0>(p) << ", " << std::get<1>(p) << "]\n";
});
subscriber.on_next(1);
subscriber.on_next(2);
subscriber.on_next(3);
subscriber.on_completed();
}Expected:
[1, 1]
[2, 2]
[3, 3]
Got:
[2, 1]
[3, 2]
Note: I used something simple for source_that_depends_on_source because something more complex would be hard to comprehend.
PS: RxJS behaves like expected (run example):
var subject = new Rx.Subject();
subject
.withLatestFrom(subject)
.subscribe(p => console.log(p));
subject.onNext(1);
subject.onNext(2);
subject.onNext(3);
subject.onCompleted();Output:
[1, 1]
[2, 2]
[3, 3]