Safe - a wrapper struct to safely access data

Abstract - Safe.md

Safe

let myNumber = 5
var mySafe = Safe(myNumber)
try mySafe.access {
  $0 += 10
  if $0 > 14 { throw SomeError.isGreaterThanFourteen }
}
print( mySafe.value )
// Prints "5"

Safe.swift

struct Safe<T> {
  private(set) var value : T
  mutating func access(_ f: (T) throws -> T) rethrows {
    var _value = try f(value)
    value = _value
  }
  mutating func access(_ f: (inout T) throws -> ()) rethrows {
    var _value = value
    try f(&_value)
    value = _value
  }
}