Add variable

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.

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'