Object Mentor Blog: Which came First?

Which came First?

Brett Schuchert — Thu, 02 Aug 2007 16:43:00 -0500

I like mnemonics. Many years ago, a colleague of mine, James, gave me a way to remember something. First I’ll give you the letters:

CCCCDPIPE

These letters are a way to remember Craig Larman’s GRASP patterns (version 1). This and knowing that in the second version of the GRASP patterns Craig replaced the D for P (D â€“ Don’t talk to strangers â€“ the Law of Demeter, P â€“ Protected Variation). By the way, here are all of them:

Coupling (low)
Cohesion (high)
Creator
Controller
Don’t talk to strangers (mentioned above and replaced with Protected Variation)
Polymorphism
Indirection
Pure Fabrication
Expert

How do I remember the letters? Well walk through this bad pun with me:

CCCC (4 c’s, foresees)
D (the)
PIPE (pipe)

So who foresees the pipe? The Psychic Plumber.

The Psychic Plumber??? I know, it’s awful. However, I heard it once in something like 1999 and I’ve never forgotten it.

That leads me to some other oldies but goodies: SOLID, INVEST, SMART and a relative new-comer: FIRST. While these are actually acronyms (not just abbreviations but real, dictionary-defined acronyms), they are also mnemonics.

You might be thinking otherwise. Typically what people call acronyms are actually just abbreviations. And in any case, they tend to obfuscate rather than elucidate. However, if you’ll lower your guard for just a few more pages, you might find some of these helpful.

Your software should be SOLID:

Single Responsibility
Open/Closed Principle
Liskov Substitution Principle
Interface Segregation
Dependency Inversion Principle (not to be confused with Dependency Inversion)

I think we should change the spelling: SOLIDD and tack on â€œDemeter â€“ the Law Of. But that’s just me. Of course if we do this, then it is no longer technically an acronym. That’s OK, because my preference is for mnemonics, not acronyms.

When you’re working on your user stories, make sure to INVEST in them:

Independent
Negotiable
Valuable
Estimable
Small
Testable

And if you’re working on tasks, make sure to keep them SMART:

Specific
Measurable
Achievable
Relevant
Time-boxed

What what is FIRST? Well have you ever heard Test Driven Development (TDD)? Some people call it by an older name, Test-First Programming (TFP). I don’t think of these as the same thing but that’s neither here nor there. What if the F in TFP really stands for FIRST (notice how I sneaked in the capitals)? If so, then here’s one possible interpretation:

Fast – tests should run fast. We should be able to run all of the tests in seconds or minutes. Running the tests should never feel like a burden. If a developer ever hesitates to execute tests because of time, then the tests tests take too long.
Isolated – A test is a sealed environment. Tests should not depend on the results of other tests, nor should they depend on external resources such as databases.
Repeatable â€“ when a test fails, it should fail because the production code is broken, not because some external dependency failed (e.g. database unavailable, network problems, etc.)
Self-Validating – Manual interpretation of results does not scale. A test should * verify that it passed or failed. Going one step further, a test should report nothing but success or failure.
Timely – tests should be written concurrently (and preferably before) with production code.

So where does this acronym come from? A while back, a colleague of mine, Tim Ottinger, and I were working on some course notes. I had a list of four out of five of these ideas. We were working on the characteristics of a good unit test. At one point, Tim said to me â€œAdd a T.â€

I can be pretty dense fairly often. I didn’t even understand what he was telling me to do. He had to repeat himself a few times. I understood the words, but not the meaning (luckily that doesn’t happen to other people or we’d have problems writing software). Anyway, I finally typed a â€œTâ€. And then I asked him â€œWhy?â€ I didn’t see the word. Apparently you don’t want me on your unscramble team either.

Well eventually he led me to see the word FIRST and it just seemed to fit (not sure if that pun was intended).

Of course, you add all of these together and what do you get? The best I can come up with is: SFP-IS. I was hoping I could come up with a Roman numeral or something because then I could say developers should always wear SPF IS – which is true because we say out of the sun and burn easily. Unfortunately that did not work. If you look at your phone, you can convert this to the number: 73747

If there are any numerologists out there, maybe you can make some sense of it.

In any case, consider remembering some of these mnemonics. If you actually do more than remember them and start practicing them, I believe you’ll become a better developer.

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"Which came First?" by Javid Jamae

Fri, 12 Oct 2007 17:33:02 -0500

I’ve always known the rule to be that if you pronounce it as a word its an acronym, and if you pronounce each letter, then it is an initialism:

http://lyberty.com/encyc/articles/abbr.html

"Which came First?" by Tim

Fri, 03 Aug 2007 13:35:46 -0500

The law still has “come into effect” if it is violated by no one. Rather, I think, you mean it is not violated.

pedantically yours, tim

"Which came First?" by Brett Schuchert

Fri, 03 Aug 2007 12:38:48 -0500

You know, I find violating it makes testing very hard (probably obvious). In reality, when I come across a large code base it probably is hard to test AND this is correlated with violation of both LOD and, typically, SRP. But something I only recently became aware of was the effect of TDD on the Law of Demeter.

In my practice, when I use TDD, which is most of the time, I find that the Law of Demeter does not really come into play. By using Test Doubles and mocking libraries, I write without long chains. Because I want to focus my test to a small unit, I plugh in other objects that offer a service rather than a chain of objects I can use. By avoiding the dependencies that make testing more difficult, I happen to not violate Demeter.

"Which came First?" by TorbjÃ¶rn Kalin

Fri, 03 Aug 2007 03:31:21 -0500

FIRST… I like it! And thanks for the summary of acronyms.

Regarding Law of Demeter: I think of it as a subset of SRP, as a means to achieve it. But then again, ISP and SRP are also very related, as well as OCP and DIP, so perhaps it’s not a bad idea to emphasize the importance of the Law of Demeter.

"Which came First?" by Brett Schuchert

Fri, 03 Aug 2007 00:11:57 -0500

Oh duh on my part. Thank you! ... I’ll fix it.

"Which came First?" by Bill Wake

Thu, 02 Aug 2007 23:22:06 -0500

T’s seem to give you trouble:) The “T” in “INVEST” is for Testable. (See http://xp123.com/xplor/xp0308/index.shtml)

"Which came First?" by Jason

Thu, 02 Aug 2007 21:25:21 -0500

Schuberry’s Greatest Hits indeed! For me personally only hearing you “ctrl-space” me to death is a founder memory than having you throw out Liskov or Law of Demeter.

Good stuff Brett. It seems a lot of developers are always looking for concise no fluff items they can print out and put in their cube wall to act as a reminder. It seems coming up with a big font version of these acronyms and mnemonics would work well.