Pitch: Multi-statement if/switch/do expressions

Evolution Pitches
399

It seems like at least one big reason people want this is to avoid reformatting during print debugging, etc. I use the following custom ~> operator based on ideas from the "With functions" pitch.:

@inlinable @discardableResult public func ~> <T>(_ value: T, modifications: (inout T) throws -> Void) rethrows -> T {
	var value = value
	try modifications(&value)
	return value
}

// Typical usage
let rect: CGRect = self.parentRect ~> { $0.size.width = 320.0 }

Besides allowing values to be modified in place, it can also be used inside of expressions to ensure they're still a single statement and avoid the parenthesis on an anonymous closure. You can simply add it to the end of the line without adding an extra return.

func doSomething(value: Int) -> Bool {
	switch value {
	case .min..<0: true
	case 0..<1000: false ~> { _ in
		print("Why did this happen?? \(value)") // Set breakpoint here 
	}
	default: true
	}
}

var goodGetter: Bool {
	self.value ~> { _ in print("Using someGetter \(self.value") }
}
var grossGetter: Bool {
	print("Using someGetter \(self.value)")
	return self.value
}
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