Xotcl April 2003

xotcl@alice.wu.ac.at

6 participants
6 discussions

Help with singleton design pattern
by Michael A. Cleverly 23 Apr '03

23 Apr '03

As I'm starting to learn XOTcl, I decided to try and implement a singleton design pattern as an educational exercise. Here is what I've come up with see below). I'd appreciate help understanding why my filterguard registration does not work as I'd expect it to. (I'd also appreciate feedback on style, or if my comments indicate a misunderstanding of what the code actually does, etc.) Thanks again for all the help. Michael #!/bin/sh # -*- tcl -*- \ exec tclsh $0 ${1+"$@"} package require Tcl 8.4 package require XOTcl 1.0 namespace import -force xotcl::* Class Singleton Singleton instproc singletonCreateFilter args { # Despite adding a filterguard (see below) for some reason # the "C foo" below would fail because a singleton instance of # class C exists ("::singletonCreateFilter" ?!??) if we don't also # check to make sure [self calledproc] == create here. # # I don't understand why ... if {[self calledproc] != "create"} { return [next] } [self class] instvar singletons set obj [lindex $args 0] set class [self] # if the object name isn't a fully qualified name make it so if {![string match ::* $obj]} { set obj [namespace parent]::$obj } # don't throw an error if we're recreating the same object if {[info exists singletons($class)] && [string equal $singletons($class) $obj] == 0} { error "Can't instantiate \"$obj\" of singleton class\ \"$class\"; \"$singletons($class)\" already instantiated" } set singletons($class) $obj next } Singleton instproc singletonDestroyFilter args { [self class] instvar singletons set class [my info class] ;# equiv of [self] info class # if other objects existed before Singleton registerClass # was called, and those objects are deleted, we don't care if {$singletons($class) == [self]} { unset singletons($class) } next } Singleton proc registerClass class { my instvar singletons my instvar registered # make sure we're dealing with a class if {[my isclass $class] == 0} { error "\"$class\" isn't a class;\ hence, can't make it a singleton class." } # Don't "double register" a class if {[info exists registered] && [lsearch -exact $registered $class] != -1} then return # We need to mixin to the object to filter the obj creation # We need to mixin to the class to filter obj destruction $class mixinappend [self] $class instmixinappend [self] $class filterappend singletonCreateFilter $class filterguard singletonCreateFilter \ {[self calledproc] == "create"} $class instfilterappend singletonDestroyFilter $class instfilterguard singletonDestroyFilter \ {[self calledproc] == "destroy"} lappend registered $class } Singleton proc create args { # doesn't make sense to instantiate objects of the singleton class error "Can't instantiate an object of \"[self]\";\ use \"[self] registerClass className\" instead." } Class C # just a quick sanity check to make sure our filter doesn't # keep us from defining instance procs or using them C instproc datetime {} { clock format [clock seconds] } Singleton registerClass C # don't expect/don't want [C foo] to fail C foo puts [foo datetime] # We expect/want [C bar] to fail C bar

4 5

info classchildren leads to a segfault
by Michael A. Cleverly 17 Apr '03

17 Apr '03

Since every class is also an object, its possible to define both procs & instprocs for it. The instprocs define methods that objects of this class will have, while the proc (as I understand it) proc would define a method on the class object, but not for objects of the class. (Yes?) However, during my interactive playing around trying different things I've found that as soon as I define a proc on the class object any subsequent use of [info classchildren] leads to a segfault. $ tclsh % package require XOTcl 1.0 % namespace import xotcl::* % Class C ::C % C info classchildren % C proc foo args {} % C info classchildren Segmentation fault Is it better to avoid defining procs on the class object, or am I misunderstanding when & where to use [info classchildren]? Michael

2 1

Static member functions?
by Michael A. Cleverly 17 Apr '03

17 Apr '03

(Disclaimer: I'm quite new to XOTcl & I have read the tutorial a couple times but maybe not enough. :-) What's the XOTcl idiom/way for a static member variable (what snit, the only other OO Tcl package/extension I've used, would call a "type variable")? Contrived example: if I had a "Chapters" class, I'd like to have a single variable, accessible by all instances of the class, that kept track of the "current" chapter. Suggestions? Michael

5 8

Multi threaded web-server in XOTcl
by Gustaf Neumann 17 Apr '03

17 Apr '03

Fellow XOTcl-community, maybe, someone finds the following code useful. The attached file implements a simple multi threaded Webserver in XOTcl that uses Zoran's the wonderful tcl thread library 2.5. It is about 150 lines of code and supports conditional requests (if-modified-since). best regards -gustaf neumann

1 0

XOTclIDE Version 0.42
by Artur Trzewik 12 Apr '03

12 Apr '03

Hallo! New release of XOTclIDE 0.42 is available on http://www.xdobry.de/xotclIDE Changes: 1) Converage Analysis Browser - The tool is based on method call tracker and It can be useful to proof the coverage of unit test. 2) Global variables inspector - help to inspect global variables (also in namespaces). Helpful to inspect pure-tcl applications 3) Wizard for importing tcl procs into XOTclIDE components from interpreter. 4) some small changes (bugs, inkonsequences) By the way. XOTclIDE will be presented on 4. European Tcl/Tk User Meeting (31.05.2003) http://www.t-ide.com/tcl2003e.html Artur Trzewik

1 0

Delegation
by Kristoffer Lawson 08 Apr '03

08 Apr '03

I've been looking at Snit recently and there are definite benefits from being able to use delegation -- it allows the combination of objects from Snit with other object-like commands in Tcl (which there are definitely quite a few of). I believe XOTcl could possibly benefit from this extra style. Naturally it would be really easy to do with filters and the unknown mechanism (as I was thinking of doing with Tk at one point), but perhaps there could be some use for an "official" approach to that. I'm not sure if this would be seen as polluting XOTcl or making it overly complex (I still believe in keeping things as simple as possible). Possibly it could be provided as a pure-XOTcl capability. Just a thought. / http://www.fishpool.com/~setok/

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Xotcl April 2003