问题描述
我正在尝试一起实现一个通用的规范模式和一个通用的访问者模式。这是我的基本接口。
export interface Specification<T,TVisitor extends SpecificationVisitor<TVisitor,T>> {
accept(visitor: TVisitor): void;
isSatisfiedBy(candidate: T): boolean;
and(other: Specification<T,TVisitor>): Specification<T,TVisitor>;
andNot(other: Specification<T,TVisitor>;
or(other: Specification<T,TVisitor>;
orNot(other: Specification<T,TVisitor>;
not(): Specification<T,TVisitor>;
}
export interface SpecificationVisitor<TVisitor extends SpecificationVisitor<TVisitor,T>,T> {
visit(specification: AndSpecification<T,TVisitor>): void;
visit(specification: AndNotSpecification<T,TVisitor>): void;
visit(specification: OrSpecification<T,TVisitor>): void;
visit(specification: OrNotSpecification<T,TVisitor>): void;
visit(specification: NotSpecification<T,TVisitor>): void;
}
为方便起见,我为基本布尔运算符实现了一些基类和一个抽象类。
export abstract class CompositeSpecification<T,T>> implements Specification<T,TVisitor> {
abstract isSatisfiedBy(candidate: T): boolean;
abstract accept(visitor: TVisitor): void;
and(other: Specification<T,TVisitor> {
return new AndSpecification<T,TVisitor>(this,other);
}
andNot(other: Specification<T,TVisitor> {
return new AndNotSpecification<T,other);
}
or(other: Specification<T,TVisitor> {
return new OrSpecification<T,other);
}
orNot(other: Specification<T,TVisitor> {
return new OrNotSpecification<T,other);
}
not(): Specification<T,TVisitor> {
return new NotSpecification<T,TVisitor>(this);
}
}
export class AndSpecification<T,T>> extends CompositeSpecification<
T,TVisitor
> {
constructor(readonly left: Specification<T,TVisitor>,readonly right: Specification<T,TVisitor>) {
super();
}
accept(visitor: TVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: T): boolean {
return this.left.isSatisfiedBy(candidate) && this.right.isSatisfiedBy(candidate);
}
}
export class AndNotSpecification<T,T>> extends CompositeSpecification<T,TVisitor> {
constructor(readonly left: Specification<T,TVisitor>) {
super();
}
accept(visitor: TVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: T): boolean {
return this.left.isSatisfiedBy(candidate) && !this.right.isSatisfiedBy(candidate);
}
}
export class OrSpecification<T,TVisitor>) {
super();
}
accept(visitor: TVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: T): boolean {
return this.left.isSatisfiedBy(candidate) || this.right.isSatisfiedBy(candidate);
}
}
export class OrNotSpecification<T,TVisitor>) {
super();
}
accept(visitor: TVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: T): boolean {
return this.left.isSatisfiedBy(candidate) || !this.right.isSatisfiedBy(candidate);
}
}
export class NotSpecification<T,TVisitor
> {
constructor(readonly other: Specification<T,TVisitor>) {
super();
}
accept(visitor: TVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: T): boolean {
return !this.other.isSatisfiedBy(candidate);
}
}
以上所有的工作和编译没有错误。但是,当我尝试创建一个扩展基本 SpecificationVisitor 接口的接口并实现一个扩展抽象 CompositeSpecification 的类时遇到编译器问题。
export interface NumberComparatorVisitor extends SpecificationVisitor<NumberComparatorVisitor,number> {
visit(specification: GreaterThan): void;
}
export class GreaterThan extends CompositeSpecification<number,NumberComparatorVisitor> {
constructor(readonly value: number) {
super();
}
accept(visitor: NumberComparatorVisitor): void {
visitor.visit(this);
}
isSatisfiedBy(candidate: number): boolean {
return candidate > this.value;
}
}
我收到以下错误:
Type 'NumberComparatorVisitor' does not satisfy the constraint 'SpecificationVisitor<NumberComparatorVisitor,number>'.ts(2344)
Interface 'NumberComparatorVisitor' incorrectly extends interface 'SpecificationVisitor<NumberComparatorVisitor,number>'.
Types of property 'visit' are incompatible.
Type '(specification: GreaterThan) => void' is not assignable to type '{ (specification: AndSpecification<number,NumberComparatorVisitor>): void; (specification: AndNotSpecification<number,NumberComparatorVisitor>): void; (specification: OrSpecification<...>): void; (specification: OrNotSpecification<...>): void; (specification: NotSpecification<...>): void; }'.
Types of parameters 'specification' and 'specification' are incompatible.
Type 'AndSpecification<number,NumberComparatorVisitor>' is not assignable to type 'GreaterThan'.ts(2430)
Type 'NumberComparatorVisitor' does not satisfy the constraint 'SpecificationVisitor<NumberComparatorVisitor,NumberComparatorVisitor>): void; (specification: OrSpecification<...>): void; (specification: OrNotSpecification<...>): void; (specification: NotSpecification<...>): void; }'.
Types of parameters 'specification' and 'specification' are incompatible.
Property 'value' is missing in type 'AndSpecification<number,NumberComparatorVisitor>' but required in type 'GreaterThan'.ts(2344)
我不太明白为什么它会抱怨。我需要改变什么才能让它按照我想要的方式工作?
解决方法
哇,里面有相当多的代码。让我们将其缩减为显示相同问题的 minimal reproducible example:
interface Foo {
ovld(x: string): number;
ovld(x: number): boolean;
}
interface BadBar extends Foo { // error!
ovld(x: boolean): string;
}
这里有一个 Foo
接口,带有一个名为 ovld
的 overloaded 方法。这个方法有两个调用签名;一个采用 string
,另一个采用 number
。我们尝试制作扩展它的 BadBar
接口。我们的目的是向 ovld
添加第三个重载,它采用 boolean
。但它不起作用!为什么?
答案是在扩展接口时不能简单地添加重载。接口扩展不是 interface merging。通过在扩展接口中重新声明 ovld
,您告诉编译器用 ovld
中的版本完全覆盖 Foo
中的 BadBar
类型。并且因为 BadBar
中的单个调用签名不能分配给 Foo
中的调用签名,这是一个错误,就像这是一个错误:
interface XXX {
prop: string;
}
interface YYY extends XXX { // error!
prop: boolean;
}
在这两种情况下,您都通过采用现有属性或方法并进行无效更改来错误地扩展接口。唯一可接受的更改是缩小更改,例如将 string
更改为 "a" | "b"
。
那么,如果我们不能仅仅通过在 ovld()
中重新声明 BadBar
来添加重载,我们如何做到这一点?一种方法是使用 indexed access type 从父接口获取现有的调用签名,然后使用新的调用签名intersect:
interface GoodBar extends Foo {
ovld: ((x: boolean) => string) & Foo["ovld"]
}
/* (property) GoodBar.ovld: ((x: boolean) => string) & {
(x: string): number;
(x: number): boolean;
} */
交集 X & Y
将被视为 X
的有效缩小,因此编译器错误消失。此外,TypeScript 认为函数的交集等同于重载。因此,上面为您提供了新的 (x: boolean) => string
调用签名作为第一个重载,然后是来自 Foo
的现有两个重载签名:
declare const goodBar: GoodBar;
goodBar.ovld(false).toUpperCase();
goodBar.ovld("hello").toFixed();
goodBar.ovld(123) === true;
万岁!
这意味着您的 NumberComparatorVisitor
可能需要更改为如下所示:
export interface NumberComparatorVisitor extends
SpecificationVisitor<NumberComparatorVisitor,number> {
visit: (
((specification: GreaterThan) => void) &
SpecificationVisitor<NumberComparatorVisitor,number>["visit"]
);
}
如果我进行了更改,那么错误就会消失,因为现在 NumberComparatorVisitor
确实是其父界面的有效扩展。