Small Type Inferencing Issue with Property<E, V> about hybrids HOT 6 CLOSED

Thanks for clarification. Feel free to re-open if you think we can do something with it.

from hybrids.

First error:

You broke the Component<CustomElement> type by mapping in your interface:

Let's fix this:

Now we have arrived at the same problem the right way

The factory(() => string) function compares two types: Property<E, V = () => string> and Property<E, V = string>
So let's simplify the task to...

type Property<T> =
  | (T extends string | number | boolean | undefined ? T : never)
  | ((lastValue: T) => T)

function factory<T>(value: Property<T>): Property<T> {
  return value;
}

// Type 'string' is not assignable to type '() => string'.ts(2322)
factory(() => "")

type ExtractOrigin<P> = P extends Property<infer Origin> ? Origin : never;


type SecondGeneric = ExtractOrigin<() => string>
// We expect `string` but `string | (() => string)` comes back!

It looks like using type unions along with conditional types breaks typescript.

And your solution actually works for this case, although it looks absurd.
I assume that after the conditional type, all other elements of the type union break down.

Therefore, conditional types need to be moved to the end of type unions throughout the code. I found several more such cases in the /** Store **/ section.

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Sent a bug report: microsoft/TypeScript#58016

from hybrids.

Typescript contributors say that this problem will not be solved in the near future, so we are solving it ourselves.

from hybrids.

Do you have a solution, which might be implemented on our side? If not, I would close the issue.

from hybrids.

The solution proposed by @au-z only works because if you have several incompatible candidates for output, then the first one is selected as the assumed type.

This solution fixes the problem in this specific use case, but may create typing errors in other use cases.

Typescript contributors will not fix this issue.

To completely solve the problem, we need to change the types significantly.

You can put this problem aside for later, I can solve it when more problems related to types appear.

from hybrids.