问题描述
我有以下错误 no instance(s) of type variable(s) R exist so that void conforms to Mono<? extends R>
。我将如何解决这个问题?我用 discord4J 在 Java 中编写了一个不和谐的机器人。当用户对相应性别 ID 的机器人表情符号做出反应时,喜欢将用户及其性别写入数据库(或在此示例中只是打印)。
public static void setUserGender(String u,ReactionEmoji e){
String gender = (e.equals(EmojiUtils.EMOJI_MALE)) ? "male" : "female";
Database.write(u,gender); // implementation prints the result for Now
}
反应命令是这样的:
public Mono<Void> issueCommand(final String[] args,final MessageCreateEvent event,final GuildSettings settings) {
Message msg = MessageUtils.sendMessage(event,"Welcome " + event.getMember().get().getNicknameMention()
+ "! It looks like you're new around here.\n No worries! "
+ "Lets get you started. What do you identify as?");
Mono<Void> maleReaction = msg.addReaction(EmojiUtils.EMOJI_MALE);
Mono<Void> femaleReaction = msg.addReaction(EmojiUtils.EMOJI_FEMALE);
Mono<Void> reactorEvent = event.getClient().on(ReactionAddEvent.class)
.filter(e -> e.getMessageId().equals(event.getMessage().getId())) // on same message
.filter(e -> e.getUserId().equals(event.getMember().get().getId())) // by same person
.next()
.flatMap(e -> Database.setUserGender(e.getUser().toString(),e.getEmoji()))
.then();
return Mono.when(reactorEvent,maleReaction,femaleReaction);
}
编辑:错误发生在这一行 .flatMap(e -> Database.setUserGender(e.getUser().toString(),e.getEmoji()))
Edit2:我尝试了使用 .flatMapMany() 的第一个建议。我收到同样的错误:
StartCommand.java:58: error: incompatible types: cannot infer type-variable(s) R
.flatMapMany(e -> Database.setUserGender(e.getUser().toString(),e.getEmoji()))
^
(argument mismatch; bad return type in lambda expression
void cannot be converted to Publisher<? extends R>)
where R,T are type-variables:
R extends Object declared in method <R>flatMapMany(Function<? super T,? extends Publisher<? extends R>>)
T extends Object declared in class Mono
解决方法
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