用对象的键作为字符串文字表示表示元组类型的类型

Question

Given an interface:

interface EPostageInsertExEvent_Parameter {
    readonly Doc: Word.Document;
    cpDeliveryAddrStart: number;
    cpDeliveryAddrEnd: number;
    readonly cpReturnAddrStart: number,
    readonly cpReturnAddrEnd: number;
    readonly xaWidth: number;
    readonly yaHeight: number;
    readonly bstrPrinterName: string;
    readonly bstrPaperFeed: string;
    readonly fPrint: boolean;
    fCancel: boolean;
}

how can I define a tuple type consisting of the keys of that interface as string literals? In other words, the equivalent of the following:

type EPostageInsertExEvent_ArgNames = ['Doc', 'cpDeliveryAddrStart', 'cpDeliveryAddrEnd',
    'cpReturnAddrStart', 'cpReturnAddrEnd', 'xaWidth', 'yaHeight', 'bstrPrinterName',
    'bstrPaperFeed', 'fPrint', 'fCancel'];

Answer 1

This is not currently possible in TypeScript. There is an feature request in GitHub which would allow this, but there hasn't been much movement there. (You might want to go and give it a 👍 and describe your use case, or you might not.) TypeScript doesn't yet have extensive support for type functions. Right now the closest you can get is:

type EPostageInsertExEvent_ArgNames = Array<keyof EPostageInsertExEvent_Parameter>;

but that does not guarantee anything about the presence, uniqueness, or order of the keys. Sorry not to have better news.