Truncate Date to Calendar.Component in Swift

I’m frequently wanting to work with truncated dates in Swift apps, especially when dealing with Swift Charts. Foundation provides Calendar.startOfDay(for:) to get the first moment of a day, and that’s been really useful. The extension below will do something similar for an arbitrary¹ Calendar.Component to truncate that date to the first moment of that component.

extension Date { /// Returns the first moment of a given Calendar.Component, as a Date. /// /// For example, pass in `.hour` called on `Date()`, if you want the start of /// the current hour of the current day. /// Supported Calendar.Components are .year, .month, .day, .hour, .minute, /// .second. Passing an unsupported component will cause `self` to be returned /// unchanged. /// Calling `.start(of: .day)` is equivalent to calling `.startOfDay`. /// - parameter to: The smallest component you want /// - returns: The first moment of the given date. func start(of component: Calendar.Component) -> Date { let allComponents =...

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