我正在尝试为 amqplib npm 包编写一个 reasonml 绑定:
http://www.squaremobius.net/amqp.node/
特别是这个功能:
http://www.squaremobius.net/amqp.node/channel_api.html#channel_get
class type amqpMessageT = [@bs] {
pub content: nodeBuffer
};
type amqpMessage = Js.t(amqpMessageT);
type gottenMessage = Js.Nullable.t(amqpMessage);
type qualifiedMessage = Message(gottenMessage) | Boolean(bool);
class type amqpChannelT = [@bs] {
pub assertQueue: string => queueParams => Js.Promise.t(unit);
pub consume: string => (amqpMessage => unit) => unit;
pub ack: amqpMessage => unit;
pub get: string => Js.Promise.t(qualifiedMessage);
pub purgeQueue: string => Js.Promise.t(unit);
pub deleteQueue: string => Js.Promise.t(unit);
pub sendToQueue: string => nodeBuffer => messageParams => unit;
};
然后我有以下代码:
....
channel##get("MyQueue")
|> Js.Promise.then_(message => {
switch message {
| Boolean(false) => Js.Promise.resolve(Js.log("No Message"));
| Message(msg) => Js.Promise.resolve(Js.log("Has Message, Will Travel"));
| Boolean(true) => Js.Promise.resolve(Js.log("Impossible Message"!));
}
}
但是,即使 js 调用返回 false,这始终会沿着“Message(msg)”路径向下移动。
现在添加以下绑定:
let unsafeGet: amqpChannel => string => Js.Promise.t(gottenMessage) = [%bs.raw{|function(channel, queueName) {
return channel.get(queueName).then((value) => {
if(value === false) {
return Promise.resolve(null)
} else {
return Promise.resolve(value)
}
})
}|}];
我已经能够回避这个问题,但bs.raw
如果我诚实的话,我并不是非常喜欢使用它。我最初的未标记联合类型有什么问题?我该如何解决这个问题?