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rosetta-abstract-type.html
Listing of doc/example-scripts/rosetta-abstract-type.tcl
Rosetta Example: Abstract type
Define a class without instances and without implemented methods. For detailed description of this example see https://rosettacode.org/wiki/Abstract_type
package req nx
Define a class AbstractQueue
nx::Class create AbstractQueue { :public method enqueue {item} {error "not implemented"} :public method dequeue {} {error "not implemented"} :public object method create {args} { error "Cannot instantiate abstract class [self]" } }
Define a concrete queue (named ListQueue) based on the Abstract Queue
nx::Class create ListQueue -superclass AbstractQueue { :variable list {} :public method enqueue {item} { lappend :list $item } :public method dequeue {} { set item [lindex ${:list} 0] set :list [lrange ${:list} 1 end] return $item } }
Demonstrating the behavior in a shell:
Trying to create an instance of the AbstraceQueue returns an error message:
% AbstractQueue new Cannot instantiate abstract class ::AbstractQueue
Create an instance of the concrete queue:
% set q [ListQueue new]
Enqueue and dequeue items
% $q enqueue 100 100 % $q enqueue 101 100 101 % $q dequeue 100