在下面的示例中，为什么` `fleet: vehicle3`没有抛出错误？

Question

想弄清楚generics的事。

我的理解是const friday:Transport<Car>将T设置为Car。

既然vehicle3的类型是Bike，为什么TypeScript不抛出错误呢？

'use strict';

interface Vehicle {
  brand: string;
}

interface Bike extends Vehicle {}

interface Car extends Vehicle {}

interface Transport<T> {
  fleet: T;
  manager: string;
}

const vehicle1: Car = {
  brand: 'Honda',
}

const vehicle2: Car = {
  brand: 'Toyota'
}

const vehicle3: Bike = {
  brand: 'Specialized'
}

const today:Transport<Car> = {
  fleet: vehicle1,
  manager: 'Cindy'
};
const tomorrow:Transport<Car[]> = {
  fleet: [vehicle1, vehicle2],
  manager: 'John'
}
const friday:Transport<Car> = {
  fleet: vehicle3,
  manager: 'Steve'
}

编辑

正如Alexey所指出的(谢谢！)，TypeScript接口是structural，因此下面的行为和我预期的一样，因为Car和Bike有冲突的属性。

'use strict';

interface Vehicle {
  brand: string;
}

interface Bike extends Vehicle {
  rider: string
}

interface Car extends Vehicle {
  driver: string
}

interface Transport<T> {
  fleet: T;
  manager: string;
}

const vehicle1: Car = {
  brand: 'Honda',
  driver: 'Alex'
}

const vehicle2: Car = {
  brand: 'Toyota',
  driver: 'Bob'
}

const vehicle3: Bike = {
  brand: 'Specialized',
  rider: 'George'
}

const today:Transport<Car> = {
  fleet: vehicle1,
  manager: 'Cindy'
};
const tomorrow:Transport<Car[]> = {
  fleet: [vehicle1, vehicle2],
  manager: 'John'
}
const friday:Transport<Car> = {
  fleet: vehicle3,
  manager: 'Steve'
}

Answer 1

这可以简化为

const v4: Car = vehicle3

TypeScript接口是结构化的，因此Vehicle、Car和Bike都是相同的。参见Type Compatibility。