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#
# == 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
package req nx::test
#
# 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 $item
}
}
# === Demonstrating the behavior in a shell:
#
# Trying to create an instance of the AbstraceQueue returns an error message:
? {AbstractQueue new} {Cannot instantiate abstract class ::AbstractQueue}
# Create an instance of the concrete queue:
? {set q [ListQueue new]} "::nsf::__#1"
# Enqueue and dequeue items
? {$q enqueue 100} 100
? {$q enqueue 101} "100 101"
? {$q dequeue} 100
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