为什么不能在接口上使用带有表达式的 C# 9

Question

我想执行以下操作（无法编译）：

public ITriggerModel UpdateDirtyTrigger(ITriggerModel dirtyTriggerModel)
{
    TriggerKey triggerKey = new(dirtyTriggerModel.Name, dirtyTriggerModel.Group);
    ITrigger trigger = _scheduler.GetTrigger(triggerKey);
    // Error: The reciever type "ITriggerModel" is not a valid record type.
    return dirtyTriggerModel with 
    {
        NextFireDateTime = trigger.GetNextFireTimeUtc(),
        PreviousFireDateTime = trigger.GetPreviousFireTimeUtc(),
        State = _scheduler.GetTriggerState(triggerKey),
    };
}

但我设法让它工作的唯一方法是使用这种可怕的代码重复：

return dirtyTriggerModel switch
{
    DailyTriggerModel daily => daily with
    {
        NextFireDateTime = trigger.GetNextFireTimeUtc(),
        PreviousFireDateTime = trigger.GetPreviousFireTimeUtc(),
        State = _scheduler.GetTriggerState(triggerKey),
    },
    WeeklyTriggerModel week => week with
    {
        NextFireDateTime = trigger.GetNextFireTimeUtc(),
        PreviousFireDateTime = trigger.GetPreviousFireTimeUtc(),
        State = _scheduler.GetTriggerState(triggerKey),
    }
};

Answer 1

with 表达式适用于记录类型。

ITriggerModel 接口可以由 class 实现，UpdateDirtyTrigger 可以用 class 类型（不是记录类型）的对象调用。