Programming Interface


OOSupport - simplify object-oriented programming in [incr Tcl]


package require Itcl
package require OOSupport

itcl::class Item {
    common attributes {
        {string   name     ""    rw}
        {bool     active   false rw}
        {number   value    0.0   rw}
        {[::Item] subitems {}    rw}

    constructor {} {

    OOSupport::bless_attributes -json_support

set sub_item1 [Item #auto]
$sub_item1 set_name   "sub item1"
$sub_item1 set_active true
$sub_item1 set_value  23.7

set sub_item2 [Item #auto]
$sub_item2 set_name   "sub item2"
$sub_item2 set_active true
$sub_item2 set_value  14.8

set main_item [Item #auto]
$main_item set_name   "main item"
$main_item set_value  1
$main_item set_subitems [list [namespace which $sub_item1] \
    [namespace which $sub_item2]]

# save main item as JSON
set json_dump [$main_item to_json]

# initialize different item from JSON
set new_item [Item #auto]
$new_item from_json $json_dump

puts [$new_item to_json]


This module provides convenience functions that allow you to define attributes on your Itcl classes and automatically generate getters, setters and support for serialization to JSON.

When defining a new type, you can declare its accessible properties in a class variable called attributes:

itcl::class Type {
    common attributes {
        {type name default access}

The type specifier should be one of bool, number, string or a class name that is recognized by itcl::is class. Additionally you can declare arrays of either type by putting the type specifier in square brackets. It is not possible to keep mixed-type arrays.

The type specifier is evaluated during serialization to or de-serialization from JSON. Since Tcl doesn't have explicit types, it would otherwise not be possible to map to and from JSON without loss of information.

After having declared the common attributes, you have to bring them to life, by calling OOSupport::init_attributes in the constructor:

    constructor {} {

This way, when an object is instantiated, member variables will be created automatically according to the attributes declaration. For an attribute name the corresponding member variable will be _name. The member variable will be initiated to the default value supplied in the attribute declaration.

Last but not least, you can bless your attributes with accessor functions according to the access specification, which can be one of

  • ro (read-only)
  • wo (write-only)
  • rw (read-write)
  • -- (no access)

The getters or setters are created by calling OOSupport::bless_attributes in the body of your class definition. If read support is enabled for an attribute name, the attribute value can be retrieved by calling a method name. If write support is enabled on the attribute, then the attribute can be set via a method set_name.

If you pass the additional parameter -json_support to bless_attributes, your objects will also have methods to_json and from_json which can be used to serialize the object state to JSON or restore an object from its JSON representation.



In a constructor, bring to life member variables according to the common attributes declaration and initialize them with specified default values.

OOSupport::bless_attributes ?-opts?

In the body of a class definition, auto-generate getter and setter methods for members according to the access specification of each attribute.

If the -json_support parameter is supplied, then objects will be blessed with additional methods to_json and from_json that allow serializing an object to and restoring it from JSON.

If -skip_undefined is specified, then empty strings and variables of other types that are initialized to null will not be included in JSON output.

If -collapse_underscore is given, then attributes of the form attr_name will be dumped and read in camel-case as attrName instead.


itcl(3itcl), json(3tcl)