Ben Finney a écrit :
Simon Hibbs <[EMAIL PROTECTED]> writes:
Orriginaly I thought I'd need to have a hull object which contains
component objects, but the component objects need access to members
of the hull object (e.g. the hull size) so that looks messy to
implement.
Was it as messy as this::
class ShipHull(object):
def __init__(self, size):
self.components = dict()
self.size = size
class ShipComponent(object):
def __init__(self, name, hull):
self.name = name
self.hull = hull
I have defined a base class Component with a class member variable
'hull_size' so that all components can see the hull size.
It seems to me the hull is an attribute of the component, and the size
is an attribute of the hull. Why would the hull size be a *class*
attribute?
I've then got two child classes called Fixed_Component and Percent
_Component that implement their mass, mass_percent and cost
properties appropriately for their type.
class FixedShipComponent(ShipComponent):
def _get_mass(self):
return calculation_foo(self.hull.size)
mass = property(_get_mass)
def _get_cost(self):
return calculation_bar(self.hull.size)
cost = property(_get_cost)
class PercentShipComponent(ShipComponent):
def _get_mass(self):
return calculation_spam(self.hull.size)
mass = property(_get_mass)
def _get_cost(self):
return calculation_eggs(self.hull.size)
cost = property(_get_cost)
Or use the strategy pattern (dummy example, don't have time to read your
specs !-):
class FixedMassCostStrategy(object):
def get_mass(self, hull):
return calculation_foo(hull.size)
def get_cost(self):
return calculation_bar(hull.size)
class PercentMassCostStrategy(object):
def get_mass(self, hull):
return calculation_spam(hull.size)
def get_cost(self):
return calculation_eggs(hull.size)
class ShipComponent(object):
def __init__(self, name, hull, masscost_strategy):
self.name = name
self._hull = hull # implementation detail
self._strategy = masscost_strategy
mass = property(lambda self: self._strategy.get_mass(self._hull))
cost = property(lambda self: self._strategy.get_cost(self._hull))
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