实现一个泛型 DeepReadonly<T>，它将对象的每个参数及其子对象递归地设为只读
您可以假设在此挑战中我们仅处理对象。不考虑数组、函数、类等。但是，您仍然可以通过覆盖尽可能多的不同案例来挑战自己
例如：
type X = {
x: {
a: 1
b: 'hi'
}
y: 'hey'
}
type Expected = {
readonly x: {
readonly a: 1
readonly b: 'hi'
}
readonly y: 'hey'
}
type Todo = DeepReadonly<X> // should be same as `Expected`
// 判断一个类型是否有键
type HasKey<T> = T extends object ? (keyof T extends never ? false : true) : false
type DeepReadonly<T> = {
readonly [K in keyof T]: HasKey<T[K]> extends true
? DeepReadonly<T[K]>
: T[K]
}
要考虑覆盖更多的类型，可以参考 Vue 源码：
type Primitive = string | number | boolean | bigint | symbol | undefined | null
type Builtin = Primitive | Function | Date | Error | RegExp
type DeepReadonly<T> = T extends Builtin
? T
: T extends Map<infer K, infer V>
? ReadonlyMap<DeepReadonly<K>, DeepReadonly<V>>
: T extends ReadonlyMap<infer K, infer V>
? ReadonlyMap<DeepReadonly<K>, DeepReadonly<V>>
: T extends WeakMap<infer K, infer V>
? WeakMap<DeepReadonly<K>, DeepReadonly<V>>
: T extends Set<infer U>
? ReadonlySet<DeepReadonly<U>>
: T extends ReadonlySet<infer U>
? ReadonlySet<DeepReadonly<U>>
: T extends WeakSet<infer U>
? WeakSet<DeepReadonly<U>>
: T extends Promise<infer U>
? Promise<DeepReadonly<U>>
: T extends {}
? { readonly [K in keyof T]: DeepReadonly<T[K]> }
: Readonly<T>