Typescript 允许对 mixins 使用适当的多重继承，但无法创建 delcaration 文件

Question

我在 TypeScript 中玩弄 "multiple inheritances" 或者更确切地说，我对 mixin 有了很好的理解。在走了很多弯路之后，我发现最简单的方法是尽可能少地进行显式转换，并且能够创建如下所示的东西（完整的示例可以在 gist 中找到）。

我的问题是：为什么 TypeScript 允许我构建它，但无法为此创建声明文件？

export function TaggedMixin<Super extends Ctor>(superClass: Super) {
  class Tagged extends superClass {
    public static TAG_PUBLIC: string;
    protected static TAG_PROTECTED: string;
    private static TAG_PRIVATE: string;

    public tag_public!: string;
    protected tag_protected!: number;
    private tag_private!: number;
  }

  return Tagged;
}

const Tagged = TaggedMixin(class {
    public static ANON_PUBLIC: string;
    protected static ANON_PROTECTED: string;
    private static ANON_PRIVATE: string;

    public anon_public!: string;
    protected anon_protected!: number;
    private anon_private!: number;
});

class TaggedClass extends Tagged {
    constructor() {
        super();

        TaggedClass.ANON_PUBLIC;
        TaggedClass.ANON_PROTECTED;
        TaggedClass.TAG_PUBLIC;
        TaggedClass.TAG_PROTECTED;

        this.anon_public;
        this.anon_protected;
        this.tag_public;
        this.tag_protected;
    }
}

编辑：

TS 无法创建声明文件的错误：

Property 'tag_protected' of exported class expression may not be private or protected.ts(4094)
Property 'tag_private' of exported class expression may not be private or protected.ts(4094)
Property 'TAG_PROTECTED' of exported class expression may not be private or protected.ts(4094)
Property 'TAG_PRIVATE' of exported class expression may not be private or protected.ts(4094)

Answer 1

发射声明和混入有限制。 Class 表达式不能有私有成员或受保护成员，因为如 here 所述：

exported anonymous classes can't have private or protected members if declaration emit is enabled, because there's no way to represent that in a .d.ts file.

Typescript 将 mixin 的实例类型表示为对象类型，并且对象类型不能具有标记为 private 或 protected 的成员，因此会出现错误。

删除非 public 成员将解决问题。

您还可以添加一些手动输入和 class 声明，这将使您接近目标：

type Ctor = new (...a: any[]) => any
declare class TaggedMixinInstance { // just a dummy, never call new TaggedMixinInstance() or extend this directly 
    public tag_public: string;
    protected tag_protected: number;
    private tag_private: number;
}

export function TaggedMixin<Super extends Ctor>(superClass: Super): {
    new(...a: any[]): TaggedMixinInstance;
    TAG_PUBLIC: string
} & Super {
    class Tagged extends superClass {
        public static TAG_PUBLIC: string;
        protected static TAG_PROTECTED: string;
        private static TAG_PRIVATE: string;

        public tag_public!: string;
        protected tag_protected!: number;
        private tag_private!: number;
    }

    return Tagged;
}

const Tagged = TaggedMixin(class {
    public static ANON_PUBLIC: string;
    protected static ANON_PROTECTED: string;
    private static ANON_PRIVATE: string;

    public anon_public!: string;
    protected anon_protected!: number;
    private anon_private!: number;
});

class TaggedClass extends Tagged {
    constructor() {
        super();

        TaggedClass.ANON_PUBLIC;
        TaggedClass.ANON_PROTECTED;
        TaggedClass.TAG_PUBLIC;
        TaggedClass.TAG_PROTECTED; // still an error

        this.anon_public;
        this.anon_protected;
        this.tag_public;
        this.tag_protected;
    }
}

Typescript 允许对 mixins 使用适当的多重继承，但无法创建 delcaration 文件

Typescript allows to use proper multiple inheritance with mixins, but fails to create delcaration files

encapsulation

multiple-inheritance

mixins

typescript