我可以定义一个Typescript映射，该映射具有与每个值的键对应的值约束吗? [英] Can I define a Typescript map having a value constraint corresponding with each value's key?

问题描述

在此游乐场我想创建一个地图，其中最多包含一个动作"联合中每种类型的单个动作.每个联合类型的区别在于具有不同的字符串文字属性"type".我为此地图定义了一个可编译但过于宽松的地图...

In this playground I would like to create a map containing at most a single action of each type in the Action union. Each of the unioned types is differentiated by having a different string literal property 'type'. I have a definition for this map which compiles but is too loose...

const lastAction:{
    [A in Action["type"]]?:Action 
} = {}

lastAction映射中的键约束强制执行...

The constraint on keys within the lastAction map enforces that...

密钥是类型"密钥.某些操作类型的属性
• 该值必须为某些操作类型

• the key is a "type" property from some Action type
• the value must be some Action type

...目前，不是强制要求键和值来自 相同 操作类型.理想地，游乐场的最后一行将由于编译器错误而失败，因为它试图分配具有"snooze"类型的动作.放入名为"fulfil"的属性中.

...it doesn't currently enforce that the key and the value are from the same Action type. Ideally the last line of the playground would fail as a compiler error as it attempts to assign an Action having type "snooze" into a property with the name "fulfil".

lastAction["fulfil"]=snoozeAction

我只是在这里想不到.我敢肯定，有一些方法可以通过分配条件或更简单的方法来做到这一点.下面的伪代码是垃圾Typescript，因为泛型无法像这样在每个属性上工作，但它可以让我了解...

I'm just missing the obvious here. I'm certain there's some way to do this with distributive conditionals or something even simpler. The pseudo-code below is junk Typescript as Generics don't work on a per property basis like this but it gives an idea of what I'm after...

const lastAction: {
    [key:A["type"]]:A extends Action
} = {};

推荐答案

使用Typescript 4.1的

With Typescript 4.1's key remapping, this is incredibly easy:

const lastAction:{
    [A in Action as A["type"]]?: A 
} = {}

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