if 0 {Richard Suchenwirth 2005-03-23 - I needed this thing to be able to backtrack a display tool, which receives instructions from a pipe on stdin. So I thought up a stack object (framework-less OO :^) with a next and a back method to walk up and down the stack, and callbacks for a data source (to extend the stack from) and "drain" (it doesn't really drain anything, it just displays it). The stack only grows over time. }
namespace eval ::IOStack {variable nextid 0}
#-- The constructor takes the names of the two callbacks, and creates a namespace for the object:
proc IOStack::IOStack {source drain} {
variable nextid
set name [namespace current]::[incr nextid]
set vars [list variable stack {} ptr -1 source $source drain $drain]
namespace eval $name $vars
interp alias {} $name {} [namespace current]::dispatch $name
# returns the name
}
#-- The dispatcher contains the methods, and is aliased to the object name
proc IOStack::dispatch {self method args} {
import $self stack ptr source drain
switch -- $method {
next {
if {[incr ptr]>=[llength $stack]} {lappend stack [$source]}
$drain $ptr:[lindex $stack $ptr]
}
back {if $ptr {$drain [lindex $stack [incr ptr -1]]}}
see {puts [list $ptr $stack] ;#-- for debugging}
default {error "bad method $method, must be 'next' or 'back'"}
}
}
#-- Utility for linking variables from a namespace
proc import {ns args} {
foreach name $args {uplevel 1 [list upvar #0 ${ns}::$name $name]}
}if 0 {The last command is the only thing here that resembles vaguely an OO "framework", except in size - if you can live without "class", "method" sugar, Tcl's namespace facility (for giving an object's instance variables a safe home) and interp alias (to redirect the popular
$object method arg...
way of calling to the generic dispatcher) are perfectly sufficient for rapid OO without any dependencies.
There is no explicit destructor - delete all traces of your stack with
namespace delete $stack
Now testing:}
set stack [IOStack::IOStack src drn]
#-- Callbacks for "source" and "drain":
proc src {} {
puts -nonewline "new data: "
flush stdout
gets stdin
}
proc drn item {
puts "draining $item"
}
#-- "keyboard event loop"
while 1 {
puts -nonewline "> "
flush stdout
gets stdin cmd
switch -- $cmd {
q {break}
+ {$stack next}
- {$stack back}
. {$stack see}
}
}See also Skeleton OO for a variant where methods are implemented as procs.