打字稿为具有推断数值的对象文字创建键约束类型

Question

假设我们有像这样的对象字面量：

export const SOURCE = {
    UNKNOWN: 'Unknown',
    WEB: 'Web',
    MOBILE: 'Mobile',
    ...
} as const;

和

export const OTHER_SOURCE = {
    UNKNOWN: 0,
    WEB: 1,
    MOBILE: 2, // values might be not sequential or incrementing at all 
    ...
} as const;
OTHER_SOURCE.UNKNOWN // inferred to 0

如何约束第二个对象文字，使其具有来自 SOURCE 的键，但值仍被推断为文字，而不是如下数字：

type ConstraintType = {
    [key in keyof typeof USER_SOURCE]: number; // how to infer (and possibly still force numbers) numeric values from the second object?
};
export const OTHER_SOURCE: ConstraintType = { ... } as const;
OTHER_SOURCE.UNKNOWN // inferred to number ]

感谢您的帮助和说明。

Answer 1

如果你指定一个变量的类型，那就是它的最终类型，所以只要右边的表达式可以赋值给它，就没问题。

如果要从分配给 OTHER_SOURCE 的对象字面量中捕获类型，但又想将其约束为具有相同的属性，则可以使用函数

export const SOURCE = {
    UNKNOWN: 'Unknown',
    WEB: 'Web',
    MOBILE: 'Mobile',
} as const;

function makeSource<T extends Record<keyof typeof SOURCE, V>, V extends number>(o: T): Readonly<T> {
  return o
}
const OTHER_SOURCE = makeSource( {
    UNKNOWN: 0,
    WEB: 1,
    MOBILE: 2, // values might be not sequential or incrementing at all  
});


OTHER_SOURCE.UNKNOWN // 1

Playground Link

打字稿为具有推断数值的对象文字创建键约束类型

Typescript create key constrained type for object literal with inferred number values

typescript

typescript-typings

type-inference

typescript-generics

literals