强类型可区分反序列化器

Question

我希望就我是否/如何利用 TypeScript 来强键入一个像这样工作的函数获得一些建议：

function createDeserializer(typeDeserializers) {
    return (data) => {
        const deserializer = typeDeserializers[data.__type];
        return deserializer(data);
    }
}

我希望能够做这样的事情：

const personDeserializer = createDeserializer({
    'employee': (data) => new Employee(data),
    'customer': (data) => new Customer(data)
});

const person1 = personDeserializer({ __type: 'employee', ... });
const person2 = personDeserializer({ __type: 'customer', ... });

// Here TypeScript knows that person1 is an 'Employee' instance, and person2 is a 'Customer' instance. 

我想我需要对 typeDeserializers 属性进行某种键映射，并以某种方式将其映射到返回值，但我有点迷茫。

Answer 1

给你

class Employee {
    constructor(data: any) {
        Object.assign(this, data);
    }
    position: string;
}
class Customer {
    constructor(data: any) {
        Object.assign(this, data);
    }
    clv: number;
}

type DeserializerTypes = { [n in string]: (data: {}) => {} };

function createDeserializer<DS extends DeserializerTypes>(typeDeserializers: DS) {
    return <T extends keyof DS>(data: { __type: T }): ReturnType<DS[T]> => {
        const deserializer = typeDeserializers[data.__type];
        return deserializer(data) as ReturnType<DS[T]>;
    }
}

const personDeserializer = createDeserializer({
    'employee': (data) => new Employee(data),
    'customer': (data) => new Customer(data)
});

const person1 = personDeserializer({ __type: 'employee' }); // inferred as Employee
const person2 = personDeserializer({ __type: 'customer' }); // inferred as Customer

console.log(person1.position);
console.log(1000 + person2.clv);

但是如果你允许反序列化器参数中的属性，但仍然希望 TypeScript 推断出确切的类型，它会变得有点棘手：

function createDeserializer<DS extends DeserializerTypes>(typeDeserializers: DS) {
    return <T extends keyof DS, D extends { __type: T }>(data: D): ReturnType<DS[D['__type']]> => {
        const deserializer = typeDeserializers[data.__type];
        return deserializer(data) as ReturnType<DS[T]>;
    }
}

const personDeserializer = createDeserializer({
    'employee': (data) => new Employee(data),
    'customer': (data) => new Customer(data)
});

const person1 = personDeserializer({ __type: 'employee', position: 'a' });
const person2 = personDeserializer({ __type: 'customer', clv: 12 }); 

console.log(person1.position);
console.log(1000 + person2.clv);