I have defined a Module with a MetaData type and a mapping object for child/nested Modules:
type Module<T, C extends Children> = {
metaData: T;
children: C;
};
type Children = {
[key: string]: Module<any, any>;
}
type ExtractMetaData<M extends Module<any, any>> = M extends Module<infer T, any> ? T : never;
type ExtractChildren<M extends Module<any, any>> = M extends Module<any, infer C> ? C : never;
Next, I create three modules, A, B, and C, where C is a child of B and B is a child of A:
type C = Module<number, {}>;
type B = Module<boolean, {
c: C;
}>;
type A = Module<string, {
b: B;
}>;
Now, I need a utility type called
AllMetaData<T extends Module>MetaData types in a Module tree. For example, AllMetaData<C> should return the type number, AllMetaData<B> should be number | boolean, and AllMetaData<A> should be number | boolean | string.
Here's my attempt at creating this type:
type AllMetaData<
MODULE extends Module<any, any>,
CHILDREN = ExtractChildren<MODULE>,
METADATA = ExtractMetaData<MODULE>,
> =
| METADATA
| {
[KEY in keyof CHILDREN]: CHILDREN[KEY] extends Module<any, any>
? ExtractMetaData<MODULE>
: never;
}[keyof CHILDREN];
However, when I try to use this type:
type Result = AllMetaData<A>;
The Result turns out to be just string, instead of the expected union of all the MetaData types in A's tree.
What could be causing this issue with my AllMetadata type?