Mixins and Traits

Mixins in Python

# Author: Daniel R. Schlegel
# Created: 4/11/2017
# A program demonstrating mixins with graph objects.

class Label(object):
    def set_label(self,label):
        self.label = label
    
    def get_label(self):
        return self.label

class Vertex(object):
    def __init__(self):
        pass
    
class LabeledVertex(Label,Vertex):
    def __init__(self,label):
        self.set_label(label)

class DirectedEdge(object): 
    def __init__(self,source,target):
        self.source = source
        self.target = target

class LabeledDirectedEdge(Label,DirectedEdge):
    def __init__(self,source,target,label):
        super(LabeledDirectedEdge,self).__init__(source,target)
        self.set_label(label)

class Graph(object):
    def __init__(self,vertices,edges):
        self.vertices = vertices
        self.edges = edges

def main():
    v1 = LabeledVertex("V1")
    v2 = LabeledVertex("V2")
    e1 = LabeledDirectedEdge(v1,v2,"rel")
    g1 = Graph(set([v1, v2]),e1)
    # Now do something with g1... 
    
if __name__ == "__main__": main()

# Author: Daniel R. Schlegel

# Created: 4/11/2017

# A program demonstrating mixins with graph objects.

class Label(object):

def set_label(self,label):

self.label = label

def get_label(self):

return self.label

class Vertex(object):

def __init__(self):

pass

class LabeledVertex(Label,Vertex):

def __init__(self,label):

self.set_label(label)

class DirectedEdge(object):

def __init__(self,source,target):

self.source = source

self.target = target

class LabeledDirectedEdge(Label,DirectedEdge):

def __init__(self,source,target,label):

super(LabeledDirectedEdge,self).__init__(source,target)

self.set_label(label)

class Graph(object):

def __init__(self,vertices,edges):

self.vertices = vertices

self.edges = edges

def main():

v1 = LabeledVertex("V1")

v2 = LabeledVertex("V2")

e1 = LabeledDirectedEdge(v1,v2,"rel")

g1 = Graph(set([v1, v2]),e1)

# Now do something with g1...

if __name__ == "__main__": main()

Traits in Scala

Scala does not support multiple inheritance, but it does support “mixing in” any number of traits. Like Java 8 interfaces they allow for partial implementation.

trait WarpShip { 
    var corePresent = true
    
    def ejectCore:Unit = {corePresent = false}
    def coreEjected:Boolean = !corePresent;
    def goToWarp(factor: Integer):Unit
    def exitWarp:Unit
}

class Starship extends WarpShip { 
  var warpFactor = 0;
  
  def goToWarp(factor: Integer):Unit = {if(!coreEjected) warpFactor = factor}
  def exitWarp:Unit = {warpFactor = 0}
}

object Main {
  def main(args: Array[String]){
    var enterprise = new Starship
    
    println("Warp " + enterprise.warpFactor);
    enterprise.goToWarp(5)
    println("Warp " + enterprise.warpFactor);
    enterprise.exitWarp
    enterprise.ejectCore
    enterprise.goToWarp(5)
    println("Warp " + enterprise.warpFactor);
  }
}

/* Output: 
 * Warp 0
 * Warp 5
 * Warp 0
 */

trait WarpShip {

var corePresent = true

def ejectCore:Unit = {corePresent = false}

def coreEjected:Boolean = !corePresent;

def goToWarp(factor: Integer):Unit

def exitWarp:Unit

}

class Starship extends WarpShip {

var warpFactor = 0;

def goToWarp(factor: Integer):Unit = {if(!coreEjected) warpFactor = factor}

def exitWarp:Unit = {warpFactor = 0}

}

object Main {

def main(args: Array[String]){

var enterprise = new Starship

println("Warp " + enterprise.warpFactor);

enterprise.goToWarp(5)

println("Warp " + enterprise.warpFactor);

enterprise.exitWarp

enterprise.ejectCore

enterprise.goToWarp(5)

println("Warp " + enterprise.warpFactor);

}

/* Output:

* Warp 0

* Warp 5

* Warp 0

See the Scala documentation page for further details.

Hi There!

Mixins in Python

Traits in Scala