Mutate Collection inside Foreach

mutate.swift

var test = [0, 1]

extension MutableCollection {
  mutating func updateEach(_ update: (inout Element) -> Void) {
    for i in indices {
      update(&self[i])
    }
  }
}

test.updateEach {
  if $0 == 1 {
    $0 = 42
  }
}

print(test) // [0, 42]