Kotlin

Question

我有一个枚举 class，看起来像这样：

enum class CommandTypes(val access: (Ctx) -> Unit, val command: (Ctx, JsonObject) -> Either<Failure, FlatResp>) {
    CREATE_DELIVERED_EVENT(adminOnly, ::createDeliveredEvent),
    CREATE_SWITCHED_EVENT(adminOnly, ::createSwitchedEvent),
    CREATE_STAMPED_EVENT(adminOnly, ::createStampedEvent),

除了command/event的类型之外，所有这些commands/events都有相同的逻辑。它们看起来都是这样的：

fun createDeliveredEvent(ctx: Ctx, json: JsonObject): Either<Failure, FlatResp> =
    validateAndCreateEvent(ctx, json, EventType.DELIVERED_EVENT)

fun createDeliveredEvent(ctx: Ctx, json: JsonObject): Either<Failure, FlatResp> =
    validateAndCreateEvent(ctx, json, EventType.SWITCHED_EVENT)

fun createDeliveredEvent(ctx: Ctx, json: JsonObject): Either<Failure, FlatResp> =
    validateAndCreateEvent(ctx, json, EventType.STAMPED_EVENT)

是否可以通过柯里化将一种类型的事件传递给命令函数，这样我就可以拥有一个接受类型的通用函数和 return 一个将类型作为参数的函数。我试过这样的事情：

fun createEvent(type:AirExpressConsignmentEventType): (ctx: Ctx, json: JsonObject) -> Either<Failure, FlatResp> =
{ ctx, json ->  validateAndCreateEvent(ctx, json, type)}

我在 CommandTypes 枚举中这样使用它 class:

CREATE_DELIVERED_EVENT(adminOnly, (::createEvent(EventType.DELIVERED_EVENT)))

但是，我得到一个错误：

This syntax is reserved for future use; to call a reference, enclose it in parentheses: (foo::bar)(args)

当我已经有了另一段使用相同语法的代码时，我不确定为什么会得到这个？

groups = (::infoGroupingWithContext)(ctx)

fun infoGroupingWithContext(ctx: Ctx): (List<Map<String, Any?>>) -> List<Map<String, Any?>> = { rows -> infoGrouping(ctx, rows) }

Answer 1

语法为

fun createEvent(type: EventType): (ctx: Ctx, JsonObject) -> Either<Failure, FlatResp> =
    { ctx, json -> validateAndCreateEvent(ctx, json, type) }

// or perhaps less confusing:

fun createEvent(type: EventType): (ctx: Ctx, JsonObject) -> Either<Failure, FlatResp> {
    return { ctx, json -> validateAndCreateEvent(ctx, json, type) }
}

// or

fun createEvent(type: EventType) = fun (ctx: Ctx, json: JsonObject): Either<Failure, FlatResp> {
    return validateAndCreateEvent(ctx, json, type)
}

但这样做可能比间接调用该函数更简洁：

enum class CommandTypes(
    val access: (Ctx) -> Unit, 
    private val type: EventType
) {
    CREATE_DELIVERED_EVENT(adminOnly, EventType.DELIVERED_EVENT),
    CREATE_SWITCHED_EVENT(adminOnly, EventType.SWITCHED_EVENT),
    CREATE_STAMPED_EVENT(adminOnly, EventType.STAMPED_EVENT);

    val command: (Ctx, JsonObject) -> Either<Failure, FlatResp>) = {
        validateAndCreateEvent(ctx, json, type)
    }
}

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