OnSet system will be triggered twice if reuse an entity ID

[eziasolsky]

Describe the bug
OnSet system will be triggered twice if reuse an entity ID

To Reproduce
with flecs 2.4.8. this is the modified "example cpp simple_system".

`
#include <simple_system.h>
#include

struct Message {
const char* text;
};

int main(int argc, char* argv[]) {
flecs::world ecs(argc, argv);

flecs::entity Likes = ecs.entity();

ecs.system<Message>()
	.kind(flecs::OnSet)
	.each([](Message& messages) {
	std::cout << messages.text << std::endl;
		});

flecs::entity Apple = ecs.entity().set<Message>({ "Apple" });
flecs::entity Bob = ecs.entity().add(Likes, Apple);
Bob.destruct();
Apple.destruct();

ecs.progress();

flecs::entity Orange = ecs.entity().set<Message>({ "Orange" });

return 0;

}
`

Expected behavior
expects
Apple Orange
but got
Apple Orange Orange

[Sander Mertens]

This issue has been fixed in v3.0 (master). Bugfixes are no longer backported to v2.4.8 as the internals have changed too much, so I recommend upgrading. I added this to the list of known issues of 2.4.8.

I do still accept PRs for 2.4.x, if you want to contribute a fix I'll merge it and create a new release. Closing the issue for now as it has been fixed in newer releases.

[eziasolsky]

I tried the same code with v3.0, but the system is not triggered at all.

[Sander Mertens]

In the v3 API you need to use a flecs::observer instead of a flecs::system. Try this code:

    ecs.observer<Message>()
        .event(flecs::OnSet)
        .each([](Message& messages) {
            std::cout << messages.text << std::endl;
        });