Typescript ques：An index signature parameter type cannot be a union type. Consider using a mapped...

写接口类型时，希望一个类型的键值是联合类型中固定的几个

const enum MSGTYPE{TEXT = 'text',IMAGE = 'image',
}
// or
// type MSGTYPE = 'text' | 'image';export interface QywxSendMessage = {msg_id: number;msg_name: string;[key: MSGTYPE]: number;
}

显然会报错An index signature parameter type cannot be a union type. Consider using a mapped object type instead. ts(1337)

问题及解决方式呢：
https://github.com/microsoft/TypeScript/issues/33440
https://github.com/Microsoft/TypeScript/issues/24220
https://github.com/Microsoft/TypeScript/issues/2491

export interface QywxSendMessage = {msg_id: number;msg_name: string;[key in MSGTYPE]: number;
}

写接口类型时，希望一个类型的键值是联合类型中固定的几个中的一个

type MSGTYPE = 'text' | 'image';export interface QywxSendMessage = {msg_id: number;msg_name: string;[key: MSGTYPE]: number;// [key: 'text' | 'image']: number;
}

显然也会报错An index signature parameter type cannot be a union type. Consider using a mapped object type instead. ts(1337)

那该如何表示呢？如果用？那显然是有问题的

type MSGTYPE<T> = {'text': T } | {'image':T };export interface QywxSendMessageParams = {msg_id: number;msg_name: string;
}export type QywxSendMessage = QywxSendMessageParams & MSGTYPE<number>;

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