Merge all possible results of a template literal union

[severe lichen]

👋 Trying some stuff with template literals:

type UnionA = { type: 'a', title: string };
type UnionB = { type: 'b', message: string };

type Both = UnionA | UnionB

type StringifyInner<K extends string | number, T> = T extends string | number ? `${K}` : Stringify<T>

type Stringify<T extends object> = {
  [K in keyof T]-?: StringifyInner<K, T[K]>;
}[keyof T];

type A = Stringify<Both>
  // ^? type A = "type"
  // I want this to be "type" | "title" | "message"

The Stringify type constrains the result to the intersection of the 2, but I want all of them

https://www.typescriptlang.org/play?#code/C4TwDgpgBAqgdgSwPZwIJQLxQN5VJALigHIBDYgGjwWABsIiBnYAJwTgHMoBfAbgCh80eMjgAhTDjzgGJAEaUoAWwiNGpDrOZtOPAYJlQxSYAAtJIlOgA+sRCjH8DkKAGVW7DggBmIAJJwcBAsADwA0lAQAB7AEHAAJoxQ2p5QtnAArkpywVQAKgB8knmRMXGJyR666Vk5LFAA-FAABgAk2GHczVBE7jpeviGFTkJuVQMgQ6WxCUlIcgBWEADGwEVY2PxQUADaEexQANYQIEjeUHkAugC0Db3jPv6BweH5e5cFAtw7x6fnV-pRugsH1PI8QsYzAUtlAAPSwqAAPQaMPhUD8UAA7qQ4MA8KYEElgEgoDkoAAiITktIU4A0ejU2zklRqDQQclAA

[feral pumice]

needs https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#distributive-conditional-types in Stringify

[severe lichen]

Thanks, @feral pumice , what should the condition extend on?

[feral pumice]

T extends any or T extends T is common

[severe lichen]

Sorry I'm not understanding, where would that go?

type Stringify<T extends object> = {
  [K in keyof T]-?: StringifyInner<K, T[K]>;
}[keyof T];

[feral pumice]

type Stringify<T extends object> = T extends T ? {
  [K in keyof T]-?: StringifyInner<K, T[K]>;
}[keyof T] : never;

[severe lichen]

Oh amazing, that works! Thanks

[vestal lantern]

!hb distribution

[pure fulcrum]

Handbook / Conditional Types

Distributive Conditional Types

[vestal lantern]

it's this btw ^

!resolved