Duplicating all of an entity's components

[WarEagle451]

The straight forward way of doing this would be to check if the entity has the component, then if so get it and copy all it's members into a new component. The issue with this way of duplicating an entity's components is that it could require a mountain of code to be written depending on how many different components could be used. Is there a better alternative for duplicating an entity's components? If not what is the best way to manage such an issue?

[skypjack]

EnTT makes heavy use of type erasure to avoid forcing users to announce their types. On the other hand, even the registry does not have a clue of the types of components used with it over time.
Because of this, technically speaking there is no way to work with a component without specifying its type, unless you prepare the right amount of erased functions to accompany an erased pool. By default, the library doesn't offer these functions. This is because the desired behavior often depends on the application and you would find yourself paying for all the instantiations required to support all the feature you don't need.

So, am I saying there is no solution for this? Quite the opposite. 🙂
But you have to dig a bit into the library and define what you need, what you want.

EnTT offers what is called a poly storage, that is, literally an empty class that you can design as you like for all types or on a per-type basis to add opaque functionalities to your pools with the desired granularity.
Something I've to document properly and to refine, but still. Here it is an example that copies the components of an entities to another entity. This is a slightly more complex example with more functionalities instead.
It's also quite easy to define a poly storage that supports copying entities and components between registries that might also have different types for their entity identifiers. Since you can (and must actually) customize everything, it goes without saying that you can do whatever you want. 🤷‍♂️

Most likely, I'll provide some pre-cooked implementations in future. Though, I'm currently working on other things because of my job, so consider this a low prio task at the moment.

[WarEagle451]

Thank you so much for the help, I had been stuck on this for quite some time now

[skypjack]

You're welcome @WarEagle451 have you been able to duplicate entities opaquely?

[WarEagle451]

I haven't got around to implementing it yet, it's a hobby project so it might be a while before I get around to it. Hopefully I'll remember to update you when I do it

[keithlostracco]

Is there an updated version of the example you linked above?

It appears that as of EnTT3.9 poly storage has been fully removed...

[keithlostracco]

Sweet! That's pretty straightforward now. Thanks.

[keithlostracco]

It turns out I was already using storage.push() (with just one arg for the destination entity) to create components so it would have the same components when I later wrote those values from a serialize function (for Undo/Redo). I didn't realize when reading the documentation for storage.push() that:

elem Optional opaque element to forward to mixins, if any.

meant I could pass the opaque values of another entity's matching component to set the values of the destination entity. Apologies, I should have read that more carefully.

[skypjack]

No worries 🙂 I'm glad it worked. 👍

[khalv]

Neither storage.push nor storage.value are defiend for me... what branch of entt does this apply to?

[skypjack]

master since a while ago. What version of EnTT are you using @khalv ?