export declare class TagProtec - CHENWL - 沸点 - 掘金

ts-ignore工程师

#每天一个知识点#
export declare class TagProtector<T extends string> {
protected __tag__: T;
}

export type Nominal<T, U extends string> = T & TagProtector<U>;

export type USD = Nominal<number, 'USD'>;

export type CNY = Nominal<number, 'CNY'>;

const CNYCount = 100 as CNY;

const USDCount = 100 as USD;

function addCNY(source: CNY, input: CNY) {
return (source + input) as CNY;
}

addCNY(CNYCount, CNYCount);

// 报错了！
addCNY(CNYCount, USDCount);

没太懂怎么实现标准化类型系统，使用联合类型为啥

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