Circling back to `with`

Evolution Pitches
26

@Erica_Sadun thank you Erica. What do you think about two other versions of the function.

  1. Extension on Any as presented above (it will work nicely with optional chaining but is similar to .dynamicType which we want to avoid)

  2. A left assignment operator instead of the with function:

precedencegroup LeftAssignmentPrecedence {
  associativity: left
  higherThan: BitwiseShiftPrecedence
  assignment: true
}

infix operator <- : LeftAssignmentPrecedence

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

According to this reply the operator can work with optional chaining.

Small example of it's usage (click to unfold) 
topGradientView <- {
  $0.prepareForAutoLayout()
  $0.attach(to: pickerHost)
  NSLayoutConstraint.activate(
    $0.topAnchor.constraint(equalTo: pickerHost.topAnchor)
      <- { $0.priority = .defaultHigh },
    $0.bottomAnchor.constraint(equalTo: backgroundView.topAnchor)
      <- { $0.priority = .defaultLow },
    $0.leadingAnchor.constraint(equalTo: pickerHost.leadingAnchor),
    $0.trailingAnchor.constraint(equalTo: pickerHost.trailingAnchor),
    $0.heightAnchor.constraint(greaterThanOrEqualToConstant: 0),
    $0.heightAnchor.constraint(lessThanOrEqualToConstant: 30)
  )
}