Rosetta example: Add a variable to a class instance at runtime

Demonstrate how to dynamically add variables to an object (a class instance) at runtime.

https://rosettacode.org/wiki/Add_a_variable_to_a_class_instance_at_runtime#Tcl

package req nx

The class Empty does not provide any structural or behaviora features on behalf of future instances, they will remain empty.

nx::Class create Empty

Provide one instance of Empty to add an object variable to …

Empty create ::e

Is e truly empty?

% ::e info vars

NX offers different types of object-variable managers: properties, variable slots, and plain Tcl per-object variables. Below, we showcase variable slots (although the others can be added dynamically alike).

a) Declare a variable slot foo; -accessor will provide getter/setter methods for this one object e automatically.

::e object variable -accessor public foo

b) Define a value for the variable slot foo

% ::e foo set 1
1

c) Is there a Tcl variable managed by the variable slot?

% ::e info vars
foo

d) Retrieve foo's value

% ::e foo get
1

A second instance of Empty has no such capability: foo

Empty create ::f

a) Is there any Tcl variable, one named foo? No …

% ::f info vars

b) Are there getter/setter methods for a foo? No …

% ::f foo set
::f: unable to dispatch method 'foo'

c) Is there a variable slot foo? No …

% ::f info object variables foo

In NX, once dynamically added, a variable slot can also be dynamically removed again.

::e delete object variable foo

a) Is the variable slot foo gone? Yes …

% ::e info object variables foo

b) Is the Tcl variable gone? Yes …

% ::e info vars

c) Are the getter/setter methods gone? Yes …

% ::e foo get
::e: unable to dispatch method 'foo'