///
/// Unwraps and returns value of optional property.
/// Returns default value if property is nil.
///
///     let integerValue: Int? = nil
///     let unwrappedValue = integerValue.unwrappedValue(defaultValue: 1)
///     print(unwrappedValue)
///     // prints 1
///
///     let integerValue: Int? = 5
///     let unwrappedValue = integerValue.unwrappedValue(defaultValue: 1)
///     print(unwrappedValue)
///     // prints 5
public func unwrappedValue(defaultValue: @autoclosure () -> Wrapped) -> Wrapped

///
/// Returns value at givent index.
/// If index is not in range of array  returns nil
///
///     let intArray: [Int] = [1,2,3,4]
///     let value = intArray[safe: 2]
///     print(value)
///     //prints Optional(3)
///
///     let intArray: [Int] = [1,2,3,4]
///     let value = intArray[safe: 10]
///     print(value)
///     //prints nil
public subscript(safe index: Int) -> Element? 
///
///
/// Returns value at given index.
/// If index is not in range of array  returns given defaultValue
///
///     let intArray: [Int] = [1,2,3,4]
///     let value = intArray[safe: 2, default: 5]
///     print(value)
///     //prints 3
///
///     let intArray: [Int] = [1,2,3,4]
///     let value = intArray[safe: 10, default: 5]
///     print(value)
///     //prints 5
public subscript(safe index: Int, default defaultValue: @autoclosure () -> Element) -> Element