Coding backwards
jameso.be
jameso.be
Works great in many cases instead of bottom up development. It really is a design methodology:
http://en.wikipedia.org/wiki/Top-down_and_bottom-up_design
You just happened to be designing as you were going along coding
People probably gloss right over it while reading unless they're personally familiar with the practice, but still have to post to HN for clarification (hint hint).
http://www.quora.com/What-is-Amazons-approach-to-product-dev...
With small or ill defined projects, throwing out bits here and there is expected - but i suspect the method can pose serious issues to larger ones.
Example : Quote of Feynman's report on the space shuttle
http://science.ksc.nasa.gov/shuttle/missions/51-l/docs/roger...
The Space Shuttle Main Engine [design] was handled in a different manner,
top down, we might say. The engine was designed and put together all
at once with relatively little detailed preliminary study of the
material and components. Then when troubles are found in the
bearings, turbine blades, coolant pipes, etc., it is more expensive
and difficult to discover the causes and make changes. For example,
cracks have been found in the turbine blades of the high pressure
oxygen turbopump. Are they caused by flaws in the material, the effect
of the oxygen atmosphere on the properties of the material, the
thermal stresses of startup or shutdown, the vibration and stresses of
steady running, or mainly at some resonance at certain speeds, etc.?
How long can we run from crack initiation to crack failure, and how
does this depend on power level? Using the completed engine as a test
bed to resolve such questions is extremely expensive. One does not
wish to lose an entire engine in order to find out where and how
failure occurs. Yet, an accurate knowledge of this information is
essential to acquire a confidence in the engine reliability in use.
Without detailed understanding, confidence can not be attained.
A further disadvantage of the top-down method is that, if an
understanding of a fault is obtained, a simple fix, such as a new
shape for the turbine housing, may be impossible to implement without
a redesign of the entire engine.That happens sometimes no matter which way you go. I've had the assumptions of what lower level libraries work off have to be completely rewritten as well because the top level system didn't make sense with the verbs and nouns given to it when you looked at it full on in the end.
The difference between redoing code gluing together lower level modules and redesigning a spacecraft make that anecdote perhaps a bit of an exaggeration on the details of work required when Top down fails.
amount = 14.,
But yes, money doesn't require floating point precision. Represent it as an integer (of cents) and add the decimal in yourself.
Also 0.025 cents per widget. Perhaps in your world 1 cent is the minimum anything in the world can cost. The rest of us, alas, live in the real world.
You might not have a 1/2p coin, but you can have 1/2p on your account.
If you want to smear a thin patina of faddishness over it, you could declare the documentation is a form of TDD, except that we're testing something that automated testing simply can't, which is the effective usability of the API from a human point of view. But then, I'm not too worried about yon thin patina of faddishness. Sometimes it's the right tool for the job, often it isn't.
If you exclusively do one or the other, you end up in bad territory. Top-Down: Results in excessively bloated API logic. Bottom-Up: You end up with a muddy API, that is overly complicated & hard to use (it's more of a RPC lib than an API).
I design the View (top down), then I design the Model (bottom up) and connect them up with the Controller.
The controller should be thin, make 1 or 2 calls to the model while mapping or cleaning input, then the response. If your controller actions are thick then your model sucks and isn't encapsulated or you have complicated response logic. Avoid these by writing great encapsulated models. understand the presenter pattern.
I've worked in sections of code that doesn't consider my opinion as advice and dechipering wtf was going on was anything but quick, and I probably introduced bugs because I couldn't understand how everything worked.
Tldr, controllers are glue code. Applications made entirely of glue doesn't even sound right saying it.
This is basically test driven development, or before that the object orient analysis. That guy interviewing you was following the object orient analysis approach. OO is sort of out of favor with all the functional fads in force.
OO Analysis is actually quite elegant, despite all the complication added later on. It can simply go by this:
1. Describe in English what your system will do. Be specific about the actors involved and their actions. e.g. Let a user projects earnings and expenses over a period of time; summarize net effect.
2. Pick out all the interesting nouns and all the verbs. The nouns become your classes and the verbs become the methods.
3. Pick out the interactions between the nouns. Added those as methods on the receiving classes. Figure out the data of the interaction, which becomes the method parameters.
From that you can do the TDD approach to build the tests to exercise the skeleton code according to your system description. And from that fill out the actual functionality of each method as you run each unit test.
I thought the same thing. Just a week ago I finished reading the "Pragmatic Unit Testing in Java" book and after skimming through the article I remembered the "design unit tests first" approach which forces you to think about the API (or exported methods).
I have not used it myself, but it seems quite sound.
The bit that rings true for me is that he decided to "write out a script using the yet unwritten API".
I have found my designs to be much more succinct & workable when instead of writing a bunch of classes then figuring out how to get them all to play together, write the code where the proverbial tyres hit the road & then go back to fill in the details.
I'm sure the more experienced software engineers out there would facePalm at this method & it's obviousness, but it gets the job done ;)
More seriously though, it all depends on what you're writing. Sometimes TDD works best, README-driven development (http://tom.preston-werner.com/2010/08/23/readme-driven-devel...) is really nice for certain projects, sometimes top-down is a good thing and sometimes just hacking away without having a clue about what you're doing turns out surprisingly well.
There's way too much discussion about methodologies and way too little about when they shine.
Unless you program every single view/controller out with no model, which means you're throwing together reams of code with no way to test it.
Interesting as a first step if you're stuck, though, but I don't see a lot of worth in this over pseudocoding the app as a design step, either.
People are angered at the number of tests relative to the size of the code base, especially if you go with something like strict 100% coverage of whitebox style tests, etc, where you're virtually guaranteed to have as many tests as function branches and then some.
Top down is an approach that has value outside the permanent test suite. You can make a more temporary suite that you use to then fill in the top down design as well, and then do not maintain.
(I am not sayings tests are bad. I'm just saying functional code is over-prioritized by some employers/customers, a well tested system is usually a good thing).
It's usually messier, though. An hour of just cleaning the code really helps as I always end up with a method that should have been broken up into 2 or more.
Um, I call that tdd.