Started by Peter Lewerin (2003-08-17).
IANAPG (I am not a patterns guru), so I use the example code from http://www.dofactory.com/Patterns/Patterns.aspx as a base for my implementations.
Chain-of-responsibility: "Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it."
package require snit
snit::type handler {
option -handleIf
variable condition false
onconfigure -handleIf value {set condition $value}
option -handleBy
variable consequent {}
onconfigure -handleBy value {set consequent $value}
option -elseReportTo
variable alternative {}
onconfigure -elseReportTo value {
set alternative [concat $value handle \$request]
}
method handle request {
if $condition $consequent $alternative
}
}Example:
proc main args {
handler Tom -handleIf {
$request >= 0 && $request < 10
} -handleBy {
puts "$self handled request $request"
} -elseReportTo Gus
handler Gus -handleIf {
$request >= 10 && $request < 20
} -handleBy {
puts "$self handled request $request"
} -elseReportTo Mary
handler Mary -handleIf {
$request >= 20 && $request < 30
} -handleBy {
puts "$self handled request $request"
}
foreach request [list 2 5 14 22 18 38 3 27 20] {
Tom handle $request
}
}Command: "Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations."
package require snit
snit::type command {
option -calculator
option -operator
option -operand
method execute {} {
[$self cget -calculator] operation [$self cget -operator] [$self cget -operand]
}
method unexecute {} {
set inverseOperator [string map {+ - - + * / / *} [$self cget -operator]]
[$self cget -calculator] operation $inverseOperator [$self cget -operand]
}
}
snit::type receiver {
variable accumulator 0
method operation {operator operand} {
set accumulator [expr [list $accumulator $operator $operand]]
puts "Total = $accumulator (following $operator $operand)"
}
}
snit::type invoker {
variable calculator
variable commands
variable current 0
method redo levels {
puts "---- Redo $levels levels"
for {set i 0} {$i < $levels} {incr i} {
if {$current < [llength $commands]} {
[lindex $commands $current] execute
incr current
}
}
}
method undo levels {
puts "---- Undo $levels levels"
for {set i 0} {$i < $levels} {incr i} {
if {$current > 0} {
[lindex $commands [incr current -1]] unexecute
}
}
}
method compute {operator operand} {
set command [command %AUTO% \
-calculator $calculator \
-operator $operator \
-operand $operand]
$command execute
lappend commands $command
incr current
}
constructor args {
set calculator [receiver %AUTO%]
}
}Example:
proc main args {
invoker user
user compute + 100
user compute - 50
user compute * 10
user compute / 2
user undo 4
user redo 3
}