count(where:)

Paul Hudson      @twostraws

SE-0220 introduced a new count(where:) method that performs the equivalent of a filter() and count in a single pass. This saves the creation of a new array that gets immediately discarded, and provides a clear and concise solution to a common problem.

This example creates an array of test results, and counts how many are greater or equal to 85:

let scores = [100, 80, 85]
let passCount = scores.count { $0 >= 85 }

And this counts how many names in an array start with “Terry”:

let pythons = ["Eric Idle", "Graham Chapman", "John Cleese", "Michael Palin", "Terry Gilliam", "Terry Jones"]
let terryCount = pythons.count { $0.hasPrefix("Terry") }

This method is available to all types that conform to Sequence, so you can use it on sets and dictionaries too.

Note: count(where:) was originally planned for Swift 5.0 way back in 2019, but was withdrawn at the time for performance reasons.

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Other changes in Swift 6.0…

• Complete concurrency enabled by default
• Typed throws
• Pack iteration
• Add Collection Operations on Noncontiguous Elements
• Access-level modifiers on import declarations
• Upgrades for noncopyable types
• 128-bit Integer Types
• BitwiseCopyable

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