打字稿只读对象文字

Question

我有一个复杂的数据模型，我需要在其中定义 40-50 个单例“元数据”对象：

• 使用歧视联合
• 有一些常规字段，但也有一个字典，它可以包含任意数量的属于歧视联盟的对象

我希望能够保留为对象文字创建的隐式类型，以便我可以使用智能感知以类型安全的方式操作这 40-50 个对象。

这是一个使用高级类型打字稿文档中的形状的示例：

interface Square {
    kind: "square";
    size: number;
}
interface Rectangle {
    kind: "rectangle";
    width: number;
    height: number;
}
interface Circle {
    kind: "circle";
    radius: number;
}
type Shape = Square | Rectangle | Circle;
type Shapes = { [x: string]: Shape };

interface Canvas { 
    name: string;
    size: number;
    //etc
}
interface Drawing extends Canvas {
    shapes: Shapes;
}

//compiles but does not give me intellisense on drawingExplicitType.shapes because it is a Dictionary 
let drawingExplicitType: Drawing = {
    name: 'myDrawing',
    size: 100,
    shapes: {
        c: { kind: "circle", radius: 1 },
        r: { kind: "rectangle", width: 1, height: 1 },
    }
};

//compiles and gives me intellisense on drawingImplicitType.shapes
let drawingImplicitType = {
    name: 'myDrawing',
    size: 100,
    shapes: {
        c: { kind: "circle", radius: 1 },
        r: { kind: "rectangle", width: 1, height: 1 },
    }
};
//will have many objects like drawingImplicitType (around 40-50) which I want to manipulate in a type safe manner
//also the shapes will have sub-shapes, so it's a tree-like data model

//I still want to be able to put all "drawing*" objects in an array of Drawing(s)
//ERROR!!! does not compile: Type 'string' is not assignable to type '"circle"'.
let drawing: Drawing = drawingImplicitType;


//## workaround ##########################################

class Drawing2 implements Canvas {
    name: string;
    size: number;
    shapes: Shapes;

    fromObjLiteral<T extends Pick<Drawing2, Exclude<keyof Drawing2, 'shapes' | 'fromObjLiteral'>> & {shapes: any}>(
        obj: T & {shapes: {readonly [x in keyof T['shapes']]: Shape}}): Drawing2 
    {
        Object.assign(this, obj);
        return this;
    }
}

//compiles and gives me intellisense on drawingImplicitType2.shapes
let drawingImplicitType2 = new (class {
    name = 'myDrawing';
    size = 100;
    shapes = new (class {
        c = new (class { readonly kind = "circle"; radius = 1 })();
        r = new (class { readonly kind = "rectangle"; width = 1; height = 1 })();
    })();
})();

let drawing2: Drawing2 = new Drawing2().fromObjLiteral(drawingImplicitType2);
let array: Drawing2[] = [drawing2];
//The workaround compiles and still allows me to make arrays of Drawing2(s) 
//But I have to create new objects and the syntax is super ugly compared to:
//let drawingImplicitType2 = readonly {...obj literal here...}

编辑 2018-05-25

正如Aleksey L.指出的那样，类型断言使用起来会更简单，但是我们需要在所有子对象上使用它们以获得强类型安全性。这对于递归树状数据模型Shape可能有点烦人，其中s 可以包含其他Shapes 但我认为它比new (class {...})()

//type assertions compile but allow me to make all kinds of errors:
let drawingTypeAssertion = {
    name: 'myDrawing',
    size: 100,
    nonExistentField: 123,
    shapes: {
        c: { kind: "circle", radiusWrongField: 1 },
        r: { kind: "rectangle", width: 1, height: 1 },
    }
};
let drawingTA: Drawing = drawingImplicitType as Drawing;

//#####################################################################
// workaround 2: deep type assertions
//#####################################################################

let drawingDeepTypeAssertion = {
    name: 'myDrawing',
    size: 100,
    nonExistentField: 123,
    shapes: {
        c: { kind: "circle", radius: 1 } as Shape,
        r: { kind: "rectangle", width: 1, height: 1 } as Shape,
    }
};
let drawingDTA: Drawing = drawingImplicitType as Drawing;
let array2: Drawing[] = [drawingDTA];
//This workaround compiles and still allows me to make arrays of Drawing2(s)
//no need to create extra objects and the syntax is a bit nicer than new (class {...})() 

结束编辑 2018-05-25

解决方法 2 的一大缺点是，一旦您这样做，as Shape您就会丢失 vscode 中的隐式类型和转到定义。

据我了解，问题来自这样一个事实，即对象文字是可变的，并且可区分的联合将不起作用。这主要是因为可变性引起的种类判别字段kind是string代替'square'或'rectangle'。

关于深度只读和“const”的讨论很多：https : //github.com/Microsoft/TypeScript/issues/10725 https://github.com/Microsoft/TypeScript/issues/15300

当前版本的打字稿是否有比上面更好的解决方法？

链接到打字稿游乐场。

Answer 1

偶然发现类似的问题并找到了另一种解决方案：

从 typescript 3.5 开始，您还可以使用const 断言，然后：

let drawingTypeAssertion = {
  name: 'myDrawing',
  size: 100,
  nonExistentField: 123,
  shapes: {
     c: { kind: "circle", radiusWrongField: 1 },
     r: { kind: "rectangle", width: 1, height: 1 },
  }
// Add this assertion here
} as const;

这将使您的所有属性变为只读。