Commented the assertion, as it prevents adding components to an entry…

[onatbas]

… in a loop of entities_with_components

When looping through entitites with entities_with_components, this assertion prevents the assignments to the entity. Such as this:

ComponentHandle<Box> boxHandle;
for (auto entity: entitiy_manager.entities_with_components(boxHandle))
{
    entity.assign<BoxPosition>();
}

It might be the design intention, but I wanted to create a pull request in case it isn't and I found the possible quick solution.

[FrankStain]

@onatbas , this code may cause the memory leak. This assert may not be removed, as far as i know.

The reason you can't add the components is because the entity already contain the requested component.

[alecthomas]

@FrankStain is correct. This assert is intentional. If you want to add the component if it's missing, you'll need to check for its existence first.