The article : <a href="https://fettblog.eu/typescript-union-to-intersection/">TypeScript: Union to intersection</a>
After reading about the contra-variance thing, I finally understand why casting <code>T</code> to function works.
Great explanation, huge kudos to the author 🎉
<pre class="shiki github-dark shaku"><code>type WrapNakedTypeWithFunction&lt;T&gt; = T extends any ? (x: T) =&gt; void : nevertype UnionToIntersection&lt;T&gt; = WrapNakedTypeWithFunction&lt;T&gt; extends (x: infer U) =&gt; void ? U : never // your code here</code></pre>

If you are just confused as me, here is a great article I found about Contra-variant type

Implement UnionToIntersection<T> to get an Intersection type from Union type. type A = UnionToIntersection<{a: string} | {b: string} | {c: string}> //…