swift - 有人可以解释为什么我在更改一行代码时收到一条错误消息，提示我缺少返回

Question

这一行没有给我任何错误:

if pendingBinaryOperation != nil && accumulator != nil {
    return (accumulator!.digit, true, pendingBinaryOperation!.description(pendingBinaryOperation!.descriptionOperand, accumulator?.literalDescription ?? " "), accumulator?.errorMessage)
} else  {
    return (accumulator!.digit, false, calculationDescription ?? "", accumulator?.errorMessage)
}

但是这一行确实给我一个错误:

if pendingBinaryOperation != nil && accumulator != nil {
    return (accumulator!.digit, true, pendingBinaryOperation!.description(pendingBinaryOperation!.descriptionOperand, accumulator?.literalDescription ?? " "), accumulator?.errorMessage)
} else if accumulator!.digit != nil {
    return (accumulator!.digit, false, calculationDescription ?? "", accumulator?.errorMessage)
}

消息是:预期返回的函数中缺少返回 '(result: Double?, isPending: Bool, description: String, errorMessage: String?)' (又名 '(result: Optional, isPending: Bool, description: String, errorMessage: Optional)' )

Answer 1

我认为在第二个代码中，你将两个返回都包装在一个“IF”中，它假设可能存在它们都不为真的情况，因此你根本不会有任何返回。