我试图创建一个基于字符串联合类型的条件类型，但是在条件类型中的最新选项出现错误2344。
// Those are available column types.
export type ColumnType =
| "boolean"
| "calculated"
| "country"
| "date"
| "enum"
| "int"
| "language"
| "price"
| "string"
// This is a template interface only used for creating column's types bellow, it won't be used elsewhere.
interface ColumnTemplate<Type extends ColumnType> {
id: string
title: string
type: Type
}
// Some column's types will have extra fiels (calculated & enum)
type CalculatedColumn<ItemType> = ColumnTemplate<"calculated"> & {
resolver: (item: ItemType) => string | null
}
type EnumColumn = ColumnTemplate<"enum"> & {
dictionary: Map<string, string>
}
type OtherType = Exclude<ColumnType, "calculated" | "enum">
type OtherColumn<Type extends OtherType> = ColumnTemplate<Type>
// This is our final column type that we want to use.
export type Column<ItemType, Type extends ColumnType> = Type extends "calculated"
? CalculatedColumn<ItemType>
: Type extends "enum"
? EnumColumn
: OtherColumn<Type>
// ^^^^ Error is here错误出现在最后一行：
Type 'Type' does not satisfy the constraint 'OtherType'.
Type 'ColumnType' is not assignable to type 'OtherType'.
Type '"calculated"' is not assignable to type 'OtherType'.(2344)OtherColumn<Type>不应为"calculated"，因为此类型应解析为CalculatedColumn ...
这里是Playground
1条答案
按热度按时间eyh26e7m1#
条件类型并不总是像我们希望的那样强大！在这个例子中，最后一行中的
Type实际上被缩小到Exclude<ColumnType, "enum">，因为内部条件，而不是我们在嵌套上下文中期望的Exclude<Exclude<ColumnType, "enum">, "calculated">。你可以通过重新排序来解决这个问题：
这是因为
EnumColumn不依赖于Type。或者，您可以使用交集显式地缩小类型：