Forum OpenACS Development: XOTcl 1.5.0 available

Hi everybody. I am pleased to announce the availability of XOTcl
1.5.0.

There is no immediate need to upgrade the XOTcl components of
oacs immediately, although new version will eventually use the new
features. One interesting feature is e.g. the partial and lazy
initialization of objects which can lead to big improvements, when an
object is initialized through multiple SQL queries, but not all
variables are not needed in each instance. The values are fetched
automatically when the variable is read the first time and are then
cached as instance variables.

The versions of xotcl-core and XoWiki are already 1.5.0-aware. Some
functionality previously defined in xotcl-core was moved to
xotcl-1.5.0. The "awareness" takes care that these methods are not
redefined, when xotcl-1.5.0 is available

Here is the full announcement.

All the best
-gustaf neumann

===================================================

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