Listing of doc/example-scripts/traits-simple.tcl
Implementation study based on
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Ducasse, O. Nierstrasz, N. Schärli, R. Wuyts, A. Black: Traits: A Mechanism for Fine-grained Reuse, ACM transactions on Programming Language Systems, Vol 28, No 2, March 2006
Example in Fig 12: ReadStream and Trait tReadStream
In this example, traits are used to extend classes and other traits.
package require nx::trait
Create a simple trait called tReadStream which provides the
interface to a stream. In contrary to a composite trait, a simple
trait does not inherit from another trait.
nx::Trait create tReadStream { # # Define the methods provided by this trait: # :public method atStart {} {expr {[:position] == [:minPosition]}} :public method atEnd {} {expr {[:position] == [:maxPosition]}} :public method setToStart {} {set :position [:minPosition]} :public method setToEnd {} {set :position [:maxPosition]} :public method maxPosition {} {llength ${:collection}} :public method on {collection} {set :collection $collection; :setToStart} :public method next {} { if {[:atEnd]} {return ""} else { set r [lindex ${:collection} ${:position}] :nextPosition return $r } } :public method minPosition {} {return 0} :public method nextPosition {} {incr :position 1} # This trait requires a method "position" and a variable # "collection" from the base class. The definition is incomplete in # these regards. :requiredMethods position :requiredVariables collection }
Define the class ReadStream with properties position and
collection that uses the trait. The method require trait checks the
requirements of the trait and imports the methods into ReadStream.
nx::Class create ReadStream { :property {collection ""} :property -accessor public {position 0} :require trait tReadStream }
Create an instance of the class ReadStream:
ReadStream create r1 -collection {a b c d e}
Test the behavior of the composed class:
% r1 atStart 1 % r1 atEnd 0 % r1 next a % r1 next b