避免将打字稿投射在开关内 [英] Avoid typescript casting inside a switch
问题描述
考虑以下代码:
interface FooBarTypeMap {
FOO: FooInterface;
BAR: BarInterface;
}
type FooBarTypes = "FOO" | "BAR";
export interface FooBarAction<T extends FooBarTypes> {
type: T;
data: FooBarTypeMap[T];
}
const doSomthingBasedOnType = (action: FooBarAction<FooBarTypes>): void => {
switch (action.type) {
case "FOO":
FooAction((action as FooBarAction<"FOO">));
}
};
const FooAction = (action: FooBarAction<"FOO">): void => {
//do something with action.data
};
现在我想避免进行强制转换(动作为FooBarAction< FOO>),如doSomthingBasedOnType,作为接口是否使之成为此开关内唯一可能性的定义。我可以在代码中进行某些更改以使其正常工作吗,或者这仅仅是TypeScript中的错误?
Now I would like to avoid the casting (action as FooBarAction<"FOO">) as seen in doSomthingBasedOnType, as the very definition if the interface makes this the only possibility inside this switch. Is there something I can change in my code for this to work, or is this simply a bug in TypeScript?
推荐答案
将 FooBarAction
转换为有区别的联合。目前,您的 FooBarAction
版本不是很严格,而 type
必须是之一 FOO | BAR
和 data
必须是 FooBarTypeMap [FooBarTypes] = FooInterface之一。 BarInterface
两者之间没有关系。因此可以允许:
You need to transform FooBarAction
into a discriminated union. At the moment your version of FooBarAction
is not very strict, while type
must be one of "FOO" | "BAR"
and data
must be one of FooBarTypeMap[FooBarTypes] = FooInterface | BarInterface
there is no relation between the two. So this could be allowed:
let o : FooBarAction2<FooBarTypes> = {
type: "BAR",
data: {} as FooInterface
}
有区别的联合版本如下:
The discriminated union version would look like this:
export type FooBarAction = {
type: "FOO";
data: FooInterface;
} | {
type: "BAR";
data: BarInterface;
}
const doSomthingBasedOnType = (action: FooBarAction): void => {
switch (action.type) {
case "FOO":
FooAction(action);
}
};
// We use extract to get a specific type from the union
const FooAction = (action: Extract<FooBarAction, { type: "FOO" }>): void => {
//do something with action.data
};
您还可以使用条件类型的分布行为从类型的并集创建并集:
You can also create a union from a union of types using the distributive behavior of conditional types:
interface FooInterface { foo: number}
interface BarInterface { bar: number}
interface FooBarTypeMap {
FOO: FooInterface;
BAR: BarInterface;
}
type FooBarTypes = "FOO" | "BAR";
export type FooBarAction<T extends FooBarTypes> = T extends any ? {
type: T;
data: FooBarTypeMap[T];
}: never;
const doSomthingBasedOnType = (action: FooBarAction<FooBarTypes>): void => {
switch (action.type) {
case "FOO":
FooAction(action);
}
};
const FooAction = (action: FooBarAction<"FOO">): void => {
//do something with action.data
};
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