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Object Adoption

In the recently released version 0.28.14 we introduced a new language feature, which is called “object adoption” — because it allows changing of an object’s parent. Every object in EO has a parent object, which is set to it when it’s born (either formed or copied). Until the recent release it was not possible to change the parent object using EO language. However, it was possible to do this from inside an atom (through Java). Now, there is no special API inside Java, but the feature is available through EO.

This is how an object is “formed”:

[id] > book
  "Object Thinking" > title

This is how we make a “copy” of it:

book 42 > b

For both of them the parent is the root object Q. You can access it using the ^ identifier:

    "The title is %s"

Now, it’s possible to create a new copy of book with a different parent:

book > x

Here, ^ (after the colon) is the name of the attribute to be bound to b. The x object created will have ^ bound to b.

It is interesting to mention that now, with the help of this new object adoption mechanism, instead of this:

a.if "left" "right"

We can do this:


Also, we can take a closed object and re-bind its ^ attribute:

b > y

Here, we create a copy of b, name it y, and reset the parent to the book object.

The objects goto, bool.while and try use object adoption mechanism. For example, when while dataizes the encapsulated body, it first adopts it:

[] > foo
  memory TRUE > x
      ^.^.write FALSE > @

Here, ^.^ points to the parent object of the parent object. The parent of the abstract anonymous object is the while object. The parent of while is x. However, it is not true until the dataization of the while starts. When the program starts, the parent of the abstract anonymous object is the foo object. It is the while object who adopts its copies after creating them.

Thus, the ^ attribute is the only mutable attribute in EO.