[英]What does the “-?” syntax mean in TypeScript mapped types?
Can anybody please explain what that "-?" 任何人都可以解释一下“ - ?” in the following TypeScript type declarations means, compared to just using a "?"
在下面的TypeScript类型声明意味着,与仅使用“?”相比 there?
那里?
type ValidationMap<T> = { [K in keyof T]-?: Validator<T[K]> }
It's not a wildcard. 这不是通配符。 The
-?
-?
notation was added in TypeScript 2.8 as a way of removing the optional modifier from mapped types. 在TypeScript 2.8中添加了表示法,作为从映射类型中删除可选修饰符的一种方法。
Basically, it means that ValidationMap<T>
has the same keys as T
, but none of the properties of ValidationMap<T>
is optional, even if the corresponding property of T
is. 基本上,这意味着
ValidationMap<T>
具有与T
相同的键,但ValidationMap<T>
任何属性都不是可选的,即使T
的相应属性是。 For example: 例如:
type Example = ValidationMap<{a: string, b?: number | undefined}>;
// type Example = {a: Validator<string>, b: Validator<number | undefined>}
Here, Example
has a required b
property even though the type it's mapped from has an optional b
property. 这里,
Example
具有必需的b
属性,即使它映射的类型具有可选的b
属性。
(Note that if you change -?
to just ?
or to +?
, it becomes the opposite... you would be adding the optional modifier. The ?
notation was added in TypeScript 2.1 as part of the mapped types feature, while the +?
notation was introduced in TypeScript 2.8 along with -?
.) (注意,如果你改变
-?
只是?
或者+?
它就会相反......你会添加可选的修饰符。 ?
作为映射类型功能的一部分,在TypeScript 2.1中添加了?
符号,而+?
符号是在TypeScript 2.8中引入的-?
。)
Hope that helps. 希望有所帮助。 Good luck!
祝好运!
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