Articles, podcasts and news about Swift development, by John Sundell.

The rule of threes

Published on 28 Jun 2018

Whenever I have 3 properties or local variables that share the same prefix, I usually try to extract them into their own method or type. That way I can avoid massive types & methods, and also increase readability, without falling into a "premature optimization" trap.

// BEFORE

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")

    let articleFolder = try contentFolder.subfolder(named: "posts")
    let articleProcessor = ContentProcessor(folder: articleFolder)
    let articles = try articleProcessor.process()

    ...
}

// AFTER

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")
    let articles = try processArticles(in: contentFolder)
    ...
}

private func processArticles(in folder: Folder) throws -> [ContentItem] {
    let folder = try folder.subfolder(named: "posts")
    let processor = ContentProcessor(folder: folder)
    return try processor.process()
}

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