[Xotcl] XOTcl 1.5.0 available

Dear XOTcl community,

I am pleased to announce the availability of XOTcl 1.5.0. To sum up, the biggest change is the introduction of slots objects, which generalize the handling of "parameters" and object class relations (like e.g. mixins). Slots provide a general and extensible interface for changing properties of objects and classes. Every multi-valued slot has e.g. a "<slot> add ..." method to add values like previously only possible for mixin and filters. Slots contain as well support for partial and lazy initialization of objects (important, when e.g. variables are initialized through costly SQL commands).

Another important change is that it is now possible to attach the predefined methods of xotcl to arbitrary objects/classes. For example, the XOTcl class system is created on the C-level completely without any methods, all methods are attached from the script initializing XOTcl.

I would like to thank the XOTcl community for many fruitful inputs and discussions, that contribute significantly to the development of XOTcl.

Best regards

-gustaf neumann

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Announcing XOTcl 1.5.0 *************************

Hi everybody. We are pleased to announce the availability of XOTcl 1.5.0. Major changes relative to 1.4.0 are:

* Improved Functionality

+ The C-level implementation of XOTcl creates now the basic classes ::xotcl::Object and ::xotcl::Class completely without any methods. All predefined methods are now registered from the initialization script-code (predefined.xotcl) via the new command

::xotcl::alias <class>|<obj> <methodName> \ ?-objscope? ?-per-object? <cmdName>

which is used for registering predefined Tcl commands as methods. These aliases are like zero cost forwarders, since they lookup the function pointer from the commands and used these in the methods.

This change makes it possible to register the same command on different classes (with maybe different names), such that for example the predefined set method of ::xotcl::Object can be replaced with a different method and the set method can be registered on some other classes (maybe some application classes).

This change makes it as well quite easy to develop some other object oriented languages based on the XOTcl framework, since all methods can be rearrange from the Tcl layer .

+ Slots

A slot is a meta-object that manages property-changes of objects. A property is either an attribute or a role of an relation.

In a nutshell, a slot has among other attributes - a name (which it used to access it), - a domain (object or class on which it can be used) , and - can be multivalued or not

Every slot defines a uniform interface to access its content. So has for example, every multivalued slot a method "add" to add a value to the list of values and a method "remove" to remove it again.

We distinguish between system slots (predefined slots like class, superclass, mixin, instmixin, filter, instfilter) and application slots (e.g. attributes of classes).

System Slots ========

System slots are predefined slots defining e.g. some relations between classes, or between objects and classes.

The predefined system slots are: - superclass: every class in XOTcl has one or more superclasses. The name of this slot is "superclass", the domain is "::xotcl::Class", the slot is multivalued. One object might have multiple superclasses. - class: every object has a class; therefore, the domain of the slot is "::xotcl::Class", the property is not multivalued. - mixin: every object in XOTcl can have one or more mixin classes. The name of this slot is "mixin", the domain is "::xotcl::Object", the slot is multivalued. - instmixin: same as above, but the domain is "::xotcl::Class" - filter, instfilter: similar to "mixin" and "instmixin"

Every slot can be used set and query the property from its domain. The syntax for setting values is <object> <property> newValue and for getting its values is set x [<object> <property>]

Every multivalued slot has as well a method "add" and "remove"

Examples for using the system slot "mixin"

Object o; Class M; class N o mixin ::M ;# replacing the per-object mixins of o with M o mixin add ::N ;# add N to the front of the mixin list o mixin delete ::M ;# delete M from the mixin list puts [o mixin] ;# query the current mixin list

Attribute Slots =========

Attribute slots are used to manage the setting and querying of instance variables. We define now a person with three attributes,"name", "salary" and "projects".

Class Person -slots { Attribute name Attribute salary -default 0 Attribute projects -default {} -multivalued true }

Examples for using the slots are

Person p1 -name "Joe" p1 projects add project1

Some additional features of the slots are:

- Support for value checking for * primitive types (all types from "string is", like integer, boolean, ...) * instances of Classes (e.g. value must be an instance of Person) * custom value checkers * uniform interface for single and multi-valued slots

- Support for lazy initialization (e.g. when costly commands (like SQL) are used to initialize instance variables, not all variables are used for each object)

- more experimental low level functionality, like * initcmd (executed, whenever the variable is read the first time) * valuecmd (executed, whenever the variable is read) * valuechangedcmd (executed, whenever the variable is altered)

For more details, see http://media.wu-wien.ac.at/doc/tutorial.html#slots

+ Re-implementation of the method "parameter" based on slots. All forms except ... -parameter {name1 {name2 default2}} ... (I.e. pure accessor parameters and parameters with defaults) are deprecated, since slots are the much more powerful and orthogonal construct.

The old c-based parameter support based on "parameterclass" is deprecated. It is still in the C-code (the method "parameter" is redefined in predefined.xotcl). If someone urgently needs it, please remove the parameter instproc from predefined for the time being, and write an email to me, in case you really need it). The C code for parameter will be removed in the next release.

+ Improved introspection though the procsearch method. This method reports now in its second argument not only [inst]proc but as well [inst]forward, [inst]parametercmd and [inst]cmd (the latter for methods implemented in C.

* Improved introspection through "info" - new subcommand "info slots" - implemented backwards bug-compatible "info parameter", deprecated

+ Improved serializer - better handling of cyclical dependencies, when mixins are involved - fix for namespace handling to make the XOTcl communication library classes working with the aolserver (thanks for Stefan Sobernig for pointing this out) - Now other ::xotcl::* objects can be included in the aolserver blueprint (e.g. non positional argument handlers) - handling of slot dependencies - more convenient calling of the serializer: Method "serialize" for Object is defined when the package xotcl::serializer is loaded.

+ Improved forwarding commands - New option for the argument substitution. When the argument list of the forward command contains "%argclindex {a b c}", then depending of the number of arguments at invocation "a", "b" or "c" is substituted. If more arguments are used at the invocation of the forwarder than values are contained in the list after %argclindex, an error is generated. - New options for forwarder: * The option -earlybinding can be used to look up the function pointer of the called Tcl command at definition time of the forwarder instead of invocation time. This option should only be used for calling C-implemented Tcl commands) * The option -verbose prints the substituted command in the forwarder prior to invocation.

+ New snit-like utility functions: - ::xotcl::myvar varName: return the fully qualified variable name of the specified variable. - ::xotcl::myproc methodName ?args?: call an xotcl method without the need of using "[list [self] methodName ...]" Both commands are namespace exported

+ added "subst" to the set of Tcl imported methods (like e.g. incr, append, ...) On can do now: % Object o ::o % o subst {I am [self]} I am ::o

+ added new method for ::xotcl::Object named "contains": This method is essentially a value added back-port of the OpenACS version. It allows to create a nested object structure with little syntactic overhead. See tutorial or language reference for more details.

* Improved code quality: + fixed a bug with nonpositional arguments, some positional arguments and "args" + fixed a bug in nonpositional arguments when called without arguments + tested with Tcl 8.4.13 and 8.5a4 + improved error messages in connection with nonpositional arguments + fixed a bug in the xotcl trace module (many thanks to jima for reporting) + fixed a namespace bug in ::xotcl::package require in connection with xotclide (many thanks to Bill Paulsen and Artur Trzewik for identifying the problem and suggesting a fix) + improved documentation (e.g. new sections added, some sections deleted, spelling improved, in total 8 pages longer) + fixed documentation bugs (many thanks for Kristoffer for reporting) + more regression tests added

For more details about the changes, please consult the ChangeLog and documentation.

MORE INFO General and more detailed information about XOTcl and its components can be found at http://www.xotcl.org

Best regards,

Gustaf Neumann Uwe Zdun