Code Smell 28 - Setters

The first exercise junior programmers do. IDEs, tutorial and senior developers keep teaching them this anti-pattern.

Problems

• Mutability

• Information Hiding

• Anemic Models

• Fail Fast

• Integrity

• Duplicated Code

Solutions

1. Avoid Setters

2. Set essential attributes on private initialization.

Sample Code

Wrong

	class PhoneCall:
	_origin = ''
	_destination = ''
	_duration = 0
	def set_origin(self, originNumber):
	self._origin = originNumber
	def set_destination(self, destinationNumber):
	self._destination = destinationNumber
	def set_duration(self, durationInSeconds):
	self._duration = durationInSeconds
	janePhoneCall = PhoneCall()
	janePhoneCall.set_origin('555-5555')
	janePhoneCall.set_destination('444-4444')
	janePhoneCall.set_duration(60)
	# Anemic and mutable Class

view raw setters.py hosted with ❤ by GitHub

Mutation brings lots of problems

	# Since you have a setter you can create invalid combinations
	janePhoneCall = PhoneCall()
	janePhoneCall.set_origin('555-5555')
	janePhoneCall.set_destination('555-5555')
	janePhoneCall.set_duration(60)
	# You can't change the destination during the call.
	# This is not enforced due to setters
	# Origin and Destination cannot be the same
	def set_destination(self, destinationNumber):
	if destinationNumber == self._origin:
	raise ValueError("Destination cannot be the same as origin")
	self._destination = destinationNumber
	def set_origin(self, originNumber):
	if originNumber == self._destination:
	raise ValueError("Destination cannot be the same as origin")
	# repeated code
	self._origin = originNumber

view raw wrongMutations.py hosted with ❤ by GitHub

Information Hiding Violated

	class PhoneCall:
	_origin = ''
	_destination = ''
	_duration = 0
	def set_duration(self, durationInSeconds):
	self._duration = durationInSeconds
	def get_duration(self):
	return self._duration
	# duration is exposed in seconds as a ripple effect
	# this violates information hiding principle
	# and prevents you from changing it representation

view raw duration.py hosted with ❤ by GitHub

Right

	class PhoneCall:
	_origin = ''
	_destination = ''
	_durationInSeconds = 0
	def __init__(self, origin, destination, durationInSeconds):
	if destination == origin:
	raise ValueError("Destination cannot be the same as origin")
	# single control point.
	# You only create valid phone calls
	# and they remain valid since they cannot mutate
	self._origin = origin
	self._destination = destination
	self._durationInSeconds = durationInSeconds
	# No setters are necessary
	def durationInSeconds(self):
	return self._durationInSeconds
	def durationInMilliSeconds(self):
	return self._durationInSeconds * 1000

view raw immutable.py hosted with ❤ by GitHub

Detection

First step will be to forbid public attributes (if language allows them).

Secondly, we will search for methods setXXXX(), analyzing method structure (should be an assignment to attribute xxxx).

We should not forbid methods setting accidental state since this is valid. They should not be named setters since they ask the object to change, but they don't set anything.

Examples

• DTOs

Exceptions

Setting attributes is safe for non-essential attributes.

But it has all drawbacks and considerations already mentioned.

Tags

• Mutation

• Information Hiding

Conclusion

Creating incomplete and anemic objects is a very bad practice violating
mutability, fail fast principle and real world bijections.

Relations

Code Smell 01 - Anemic Models

Maxi Contieri ・ Oct 20 '20

#codenewbie #oop #beginners #computerscience

More Info

Fail Fast

Here is the full discussion on Setters

Credits

Photo by Victor Rodriguez on Unsplash

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Object-oriented programming languages support encapsulation, thereby improving the ability of software to be reused, refined, tested, maintained, and extended. The full benefit of this support can only be realized if encapsulation is maximized during the design process.

Rebecca Wirfs-Brock