在 TypeScript 中切换特定类型 [英] Switch for specific type in TypeScript

问题描述

我有一个接口Action:

interface Action {}

以及这个Action的实现SpecificAction:

class SpecificAction implements Action {
   payload?: Any
}

是否可以在 TS 中构造 switch 运算符，如下所示:

Is it possible in TS to construct a switch operator, like this:

let action: Action
switch (action) {
   case SpecificAction: //it works
       console.log(action.payload) // it doesn't 
}

在这种情况下，是否有可能知道该操作已经属于 SpecificAction 类型?

Is it possible in that case to know, that action is already of SpecificAction type?

推荐答案

目前看来有几个选项，但都有一些缺点

for the time being it looks like there are a few options, all of them with some drawbacks

• 歧视工会docs stackblitz，但您需要一个专用属性作为鉴别器

• discriminated unions docs stackblitz, but you'll need a dedicated property as discriminator

interface Action {}

class SpecificAction implements Action {
  kind: "specific";
  payload?: any;
}

class ToggleAction implements Action {
  kind: "toggle";
  toggle: boolean;
}

let action: SpecificAction | ToggleAction;
switch (action.kind) {
  case "specific":
    console.log(action.payload) // it works 
    break;
  case "toggle":
    console.log(action.toggle) // it works 
    break;        
}

• 用户定义的类型保护 docs stackblitz，但你需要 if 语句而不是 switch
• User-Defined Type Guards docs stackblitz, but you'll need if statements instead of switch

interface Action {}

class SpecificAction implements Action {
  payload?: any;
}

class ToggleAction implements Action {
  toggle: boolean;
}

let isSpecific = (p: any): p is SpecificAction => !!p.payload
let isToggle = (p: any): p is ToggleAction => !!p.toggle

let action: Action;
if (isSpecific(action)) {
  console.log(action.payload) // it works 
} else if (isToggle(action)) {
  console.log(action.toggle) // it works 
}

• 构造函数属性 github stackblitz，但您需要暂时转换为所需的类型
• constructor property github stackblitz, but you'll need to cast to desired type for the time being

interface Action { }

class SpecificAction implements Action {
  payload?: any;
}

class ToggleAction implements Action {
  toggle: boolean;
}

switch (action.constructor) {
  case SpecificAction:
    console.log((<SpecificAction>action).payload) // it kinda works 
    break;
  case ToggleAction:
    console.log((<ToggleAction>action).toggle) // it kinda works 
    break;
  }

这篇关于在 TypeScript 中切换特定类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！