[FEATURE REQUEST] Modify CopyComponentTo code-gen for better copying

[jeffcampbellmakesgames]

Is your feature request related to a problem? Please describe. Currently the entity API CopyComponentTo performs a shallow copy of a component where a template instance's members's vales are assigned to a new component instance's members. This results in reference types being assigned directly, thus maintaining the reference instance of the same member between two different component instances. This includes members that are collections where the instance of the collection is assigned to both component instances. There is not currently an option that enables for deep copying a reference type member and/or copying the contents of a list to a new component collection member rather than assigning the collection itself.

Describe the solution you'd like Ideally, the outcome of a reference type member on a component being copied should be:

• By default pass the member by reference.
  • For member types derived from MonoBehaviour or ScriptableObject (really anything from UnityEngine.Object) the intent is more likely to assign by ref since they usually don't have a default constructor or straightforward way to copy over all the instance data.
  • For member types that are plain-old CSharp objects, work from the developer is needed to copy over all required data on the component to a new instance, particularly where they could also contain Unity object member types.
• When a member reference type implements ICloneable, rather than assign the ref value directly call the Clone method on assignment to create a new separate instance of that ref type. By implementing ICloneable on a type used as a member on a component, in effect that will result in CopyComponentTo deep-copying the ref instance to a new one.
• When a member type is a collection:
  • If its an IList, IReadOnlyList, iterate over the list item in a for loop and assign/copy each member using these same default/ICloneable, collection rules.
  • If its not an IList, IReadOnlyList, iterate over the collection in a foreach loop and assign/copy each member using these same default/ICloneable, collection rules.

Describe alternatives you've considered I'd like to avoid heavy usage of runtime reflection as much as possible to reduce down on the performance hit this operation should take (especially since it has the capacity to be used in bulk for many entities from blueprints). Any reflection that takes place should either be small or cached for reuse.

Tasks

• [x] Implement ICloneable on several example ref type components
• [x] Add ICloneable code-generation logic for CopyComponentTo method code-generator
• [x] Add List code-generation logic for CopyComponentTo method code-generator
• [x] Add Array code-generation logic for CopyComponentTo method code-generator
• [x] Add Dictionary code-generation logic for CopyComponentTo method code-generator
• [x] Add unit tests for TypeExtensions to validate functionality
• [x] Add unit tests for CopyComponentTo method to validate functionality
• [x] Update documentation

[jeffcampbellmakesgames]

Accomplished much of the implementation for a more nuanced copy logic for component members based on whether they are capable of supporting deep copy logic or not, looking to update/create unit tests and update documentation.

[jeffcampbellmakesgames]

This has been merged to develop.