我有一个带有BaseParams
构造函数参数的Base
类,并且希望从Base
扩展一个Derived
类,该类接受ExtendedParams
构造函数参数,并将其传递给super()
,以及一些默认值。问题是,我似乎找不到Derived
构造函数参数的访问修饰符和类型的正确组合。
到目前为止,我拥有的是:
interface BaseParams {
first: string;
}
interface ExtendedParams extends BaseParams {
last?: string;
}
class Base {
constructor(protected params: BaseParams) {}
inspect(): void {
console.log(this.params);
}
}
class Derived extends Base {
constructor(??? params ???) {
super({ first: 'John', last: 'default', ...params }); // override default params with specified ones
this.params.last; // #1 - this should not generate any compile errors
this.params.whatever = 'Wrong'; // #2 - TS should flag this as not existing on type ExtendedParams
}
}
const d = new Derived({ first: 'Mike' });
d.inspect(); // #3 - should output { first: 'Mike', last: 'default', whatever: 'Wrong' }
我尝试将Derived
params
声明为protected
。这就解决了问题1和问题2。
class Derived extends Base {
constructor(protected params: ExtendedParams) {
super({ first: 'John', last: 'default', ...params });
this.params.last; // #1 - ok, no error
this.params.whatever = 'Wrong'; // #2 - ok, flagged: `whatever` doesn't exist on type ExtendedParams
}
}
问题是last: 'default'
赋值没有发生,因为protected
生成的this.params = params
赋值覆盖了传递给super()
的params
值,所以d.inspect()
只输出{ first: 'Mike', whatever: 'Wrong' }
。
我尝试省略params
的访问修饰符。这导致正确的输出{ first: 'Mike', last: 'default', whatever: 'Wrong' }
,但也导致this.params.last
被标记为错误does not exist on type 'BaseParams'
。
class Derived extends Base {
constructor(params: ExtendedParams) {
super({ first: 'John', last: 'default', ...params });
this.params.last; // #1 - wrong ly flagged
this.params.whatever = 'Wrong'; // #2 - ok, flagged
}
}
是否有一些TypeScript魔术可以通知编译器,在Derived
类中,this.params
是ExtendedParams
类型,和默认值将传递给super()
调用,之后this.params
不会被覆盖?
但是从Derived
访问Base.params
,它被明确地键入为BaseParams
。
如果您希望params
属性更改派生类中的类型,则需要一个泛型基类型:
// <P = BaseParams> allows to instantiate Base with BaseParams as default type.
class Base<P = BaseParams> {
constructor(protected params: P) {}
/* ... */
}
class Derived extends Base<ExtendedParams> {
constructor(params: ExtendedParams) {
super({ first: 'John', last: 'default', ...params }); // override default params with specified ones
this.params.last; // OK
this.params.whatever = 'Wrong'; // Wrong
}
}