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Betwist(tm): Evolutionary Design of a Trie
I’m building Betwist(tm), a word-finding game related to Boggle®. You’re given a repeating grid of letters, and find words by moving from letter to letter. We start with a dictionary, the set of all...
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AAA and the Object Lifecycle
We’ll look at how Arrange-Act-Assert (AAA) tests reflect the lifecycle of the objects we’re working with. Object Lifecycle An object has a basic lifecycle: create (command | query)* (abandon | delete)...
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“Test Interface, Not Implementation”
“Test Interface, Not Implementation” Perhaps you’ve heard the phrase “Test interface, not implementation”, or its relative, “Test behavior, not implementation”. We’ll look at this from the TDD...
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How to Reduce Coupling, Three Ways
Two objects are coupled if changing one requires us to change the other. (See Yourdon and Constantine.) We’d like to reduce coupling, since it makes changing code more complicated. A change in a...
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Reordering Items, Four Ways
Recently I needed to implement a drag-and-drop reordering, with persistence. At least with SwiftUI, reordering is easy if it’s all in memory: you have an array of items, the UI tells you which ones...
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And-Or Trees
Suppose you want to represent a finite set of possibilities in a compact way. An And-Or Tree can do this, and is useful in several situations. An And-Or Tree has leaf nodes and interior nodes. The...
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Run Tests Without an App — Step by Step with Xcode
I’m frustrated when unit tests run slowly. One way to speed them up in Xcode when developing using a simulator: isolate your model to a framework, and run your tests without a host application....
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Swift Testing – A New Unit Testing Framework
Apple has introduced a new unit testing framework. It has a simpler syntax, much simpler assertions, parameterized testing, and more. Let’s take a look. You can find a bonus cheatsheet at the end of...
View ArticleTDD with a Function Pipeline
Our “geek” group tackled a problem a couple weeks ago, that one of us had heard suggested by Michael Feathers: given a sequence of numbers, tell how many non-zero runs it has. Ron Jeffries described a...
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Trees – Confidence in Design
Test-Driven Development (TDD) depends on assembling well-tested parts into a trustworthy whole. Some design structures make this easier. Today, we’ll look at trees. A tree is a structure consisting of...
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Pipelines – Confidence in Design
The other day, Kent Beck pointed out a skill that test-driven development (TDD) relies on but doesn’t give much guidance about: “behavioral composition”. This is the skill of dividing a big behavior...
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Threaded Code (and Composite)
Let’s look at the threaded code approach. It’s a less-well-known way to build an interpreter for a programming language. (The more common approach simulates each instruction.) Threaded code has a...
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Time Troubles – Transitions
Time is a well-known source of trouble for programmers. We looked earlier at one type of time troubles: overflow. Today, I’d like to look at another time trouble: transitions. Here are the problems...
View ArticleRefactor: Inline-Adjust-Extract
Sometimes, we feel that something we extracted isn’t as good as it could be. The Inline-Adjust-Extract refactoring pattern can help fix that. It has three steps: Inline: put the extracted code back...
View ArticleOrganizing Fields and Methods
When you’re making a class, in what order do you put the fields and methods? We’ll look at several choices and some tradeoffs between them. Organizing Fields I’ve seen a few approaches to organizing...
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Reduce Dependencies Using Lambda
When A depends on B (A → B), a change in B may force A to change as well. Dependencies are both good and bad: they let objects work together, but they make software harder to change. We can use lambda...
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Iterative Enhancement and XP-Style Design
“Iterative Enhancement” is a model for iterative development, from Basili & Turner, described in 1975 (!). We’ll look at it, and compare it to XP’s approach. I’ve seen occasional mention of this...
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Refactoring: Extract Local Lambda
Extracting a local lambda turns a block of code into an anonymous inline function. Motivation A local lambda can isolate code for improvement (the Isolate-Improve-Inline pattern – see References), or...
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Refactoring: Replace Method with Method Object
Sometimes, when you try to break up a long method, you run into a problem: you have to pass a bunch of local variables into the new method, some of which are both input and output. One solution is the...
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A Dead End for Evolutionary Design
In traditional design, you identify the capabilities and characteristics of a planned system, then create an overall design that accommodates them. In evolutionary design, you grow the system one...
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