带有嵌套属性的打字稿判别联盟，有很多可能性清单

Question

我在几个地方读到，目前与嵌套属性有判别的工会是不可行的，或者至少没有防护功能是不可行的，我想知道是否有一种根本不使用后卫功能来确定类型的方法。

目的是尝试使用枚举来缩小缩小，因为多个customfieldtype可以具有相同类型的value，并且每次使用Switch语句每次注册案例都会更简单而不是if-elseif要缩小。

Here is a typescript playground that tries the different possibilities.

enum CustomFieldType {
    INT = 'int',
    STRING = 'string',
    MULTISELECT = 'multiselect',
    SELECT = 'select'
    // Possibly 20 others
}

interface CustomFieldValueBase<T extends CustomFieldType> {
    customField: {
        type: T;
    }
    value: any;
}

interface CustomFieldValueInt extends CustomFieldValueBase<CustomFieldType.INT> {
    value: number;
}
interface CustomFieldValueString extends CustomFieldValueBase<CustomFieldType.STRING> {
    value: string;
}
interface CustomFieldValueMultiSelect extends CustomFieldValueBase<CustomFieldType.MULTISELECT> {
    value: number[];
}
interface CustomFieldValueSelect extends CustomFieldValueBase<CustomFieldType.SELECT> {
    value: number[];
}

type CustomFieldValue =
  | CustomFieldValueInt
  | CustomFieldValueString
  | CustomFieldValueMultiSelect
  | CustomFieldValueSelect


// Solution wanted
// Won't narrow
function guessType(cfv: CustomFieldValue) {
    switch (cfv.customField.type) {
        case CustomFieldType.INT:
            return cfv.value // should be narrowed to number
        case CustomFieldType.STRING:
            return cfv.value // should be narrowed to string
        case CustomFieldType.MULTISELECT:
        case CustomFieldType.SELECT:
            return cfv.value // should be narrowed to number[]
        default: throw new Error()
    }
}