Abstract keyword for scripts

[GianptDev]

Describe the project you are working on

.

Describe the problem or limitation you are having in your project

.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Can the engine implement abstract classes/scripts like other languages such as java do?

It can help the user to tell the user a specific class is a base class not intended to be used but only to be extended.

It could be implemented adding the abstract keyword to a script like tool does, and should:

• not allow to instance the script with new()
• allow to load the script using load(), preload(), or globally via class_name
• allow to extend the script and when extended abstraction is removed in the new script unless is define again.

Can be used to make a parent class that define only the base code of sub-classes and allow only those sub-classes to be used.

Action (abstract)
├── ActionMove
├── ActionScale
└── ActionRotate

Here an example of a robot that could move by a list of actions, adding actions like movement and rotation makes sense:

var robot: = MovableThing.new();
robot.add_movements(
    ActionMove.new(12, 0), # move the thing by 12 on x axys.
    ActionRotate.new(90),   # rotate the thing
    Action.new() # empty action, it does nothing and we could tell the used this is useless.
);

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

The keyword could be used like this:

# script marked as abstract, cannot be instanced.
abstract class_name SomeClass extends Object;
# ...

Will prevent to instance the abstract class.

SomeClass.new(); # this will result in an error.

But allow extends:

class_name AnotherClass extends SomeClass;
# abstraction resetted.

And can be used to implement a list of global constant properties and mark that instancing this object is useless.

abstract class_name Globals extends Object;

const foo = "bar";
# ...

Maybe even adding a function to the Script object to check if the script has the abstract flag:

var someScript: Script = load("path/to/script.gd");
someScript.is_abstract(); # true of false.

If this enhancement will not be used often, can it be worked around with a few lines of script?

.

Is there a reason why this should be core and not an add-on in the asset library?

yes

[Mickeon]

Duplicate of #5641.