"""
MakeAClassHierarchy.cobra
This HowTo shows the syntax for classes, inheritance, initializers, properties,
defining toString, unit tests and so forth.
The class hierarchy is:
Object
Vehicle
Aircraft
Plane
Train
Automobile
"""
enum Medium
"""
Defines the various mediums that a vehicle can travel through.
"""
belowWater
aboveWater
land
air
space
class Vehicle
test
v = Vehicle()
assert not v.isMoving
assert not v.hasMoved
assert v.serialNum > 0
v.startMoving
assert v.isMoving
assert not v.hasMoved # because no miles accumulated
v.move(5)
assert v.isMoving
assert v.hasMoved
assert v.numMiles == 5
v.move(3)
assert v.numMiles == 8
v.stopMoving
assert not v.isMoving
assert v.hasMoved
w = Vehicle()
assert v.serialNum <> w.serialNum
shared
var __nextSerialNum = 1001
var _serialNum as int
var _isMoving = false
var _numMiles = 0.0
def init
_serialNum = __nextSerialNum
__nextSerialNum += 1
get serialNum from var
# `get` defines a read-only property.
# `from var` is a shortcut syntax to cover
# the variable with the matching name.
get hasMoved as bool
return _numMiles > 0
get isMoving from var
get numMiles from var
def startMoving
assert not _isMoving, 'Already moving.'
_isMoving = true
def move(distance as decimal)
assert _isMoving, 'Invoke startMoving first.'
assert distance > 0
_numMiles += distance
def stopMoving
assert _isMoving, 'Not moving.'
_isMoving = false
def canTravelIn(medium as Medium) as bool
"""
Returns true if the given medium is the primary medium that the vehicle
normally travels through.
"""
return false
def toString as String is override
test
v = Vehicle()
sn = v.serialNum
assert v.toString == 'Vehicle([sn])'
body
sb = StringBuilder()
sb.append('[.getType.name]([_serialNum]') # example: 'Foo(1001)'
.buildString(sb) # so subclasses can add their fields
sb.append(')')
return sb.toString
def buildString(sb as StringBuilder)
"""
Invoked by `toString` so that subclasses can add their information.
Subclasses should normally invoke base.
"""
pass
class Aircraft
inherits Vehicle
def canTravelIn(medium as Medium) as bool is override
return medium == Medium.air
class Plane
inherits Aircraft
class Train
inherits Vehicle
var _numUnits = 0
"""
The number of locomotives and railroad cars in the train.
"""
def init(numUnits as int)
base.init
assert numUnits > 0
_numUnits = numUnits
get numUnits from var
def canTravelIn(medium as Medium) as bool is override
return medium == Medium.land
def buildString(sb as StringBuilder) is override
base.buildString(sb)
sb.append(', [_numUnits] units')
class Automobile
inherits Vehicle
def canTravelIn(medium as Medium) as bool is override
return medium == Medium.land
class Program
def main is shared
# create some vehicles
p = Plane()
t = Train(5)
a = Automobile()
vehicles = [p, t, a] # a list
for v in vehicles
assert v.serialNum > 0
print v |