Throw if nil, otherwise return value

ThrowIfNil.swift

infix operator ??!: NilCoalescingPrecedence

/**
 If the left-hand side in nil, the error on the right-hand side is thrown. Otherwise,
 the unwrapped value is returned. For example:
 
 ```
 // Instead of this…
 
 guard let x = y else {
  throw SomeError.someError
 }
 
 // You can say this…
 let x = try y ??! SomeError.someError
 ```
 */
@discardableResult func ??!<T>(lhs: T?, rhs: @autoclosure () -> Error) throws -> T {
    guard let lhs = lhs else {
        throw rhs()
    }
    return lhs
}