Intersection will be splited when wrap a tuple and use `extends` tuple.

[NWYLZW]

🔎 Search Terms

• intersection
• Distributive Conditional Types
• union

🕗 Version & Regression Information

• This changed between versions 4.1.5 and 5.3.2

⏯ Playground Link

https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmYcDCEA2ngGMYAMAPACoA0cAqgHxwC8cJcoMwAdgCYDOcA2gLpwA-HDbAAbsChwAXHyYAyKvwBQoSLATJUGbHhgBGUhRr15cJZVUqkKRgTMAKA3AA+cAExu4AcgDMPgCUFqIArgC2AEZSKgD0sXCJAHpCNtqMLgy6OPjELu5e7n7ePgAsPhRsEdFQ1HEJyam2qCReWVg5hkT5nt7F7mUVYVFSdfGJcCkqQA

💻 Code

export type Collect0<T, U> = T extends [] ? never : [T & U]
export type Collect1<T, U> = [T & U]

type T0 = (1 | 2 | '3') & number
//   ^? type T0 = 1 | 2
type T1 = Collect0<1 | 2 | 3 | '4', number>
//   ^? type T1 = [never] | [1] | [2] | [3]
type T2 = Collect1<1 | 2 | 3 | '4', number>
//   ^? type T2 = [1 | 2 | 3]

🙁 Actual behavior

type T1 = Collect0<1 | 2 | 3 | '4', number>
//   ^? type T1 = [never] | [1] | [2] | [3]

🙂 Expected behavior

type T1 = Collect0<1 | 2 | 3 | '4', number>
//   ^? type T1 = [1 | 2 | 3]

Additional information about the issue

No response

[fatcerberus]

Working as intended. https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#distributive-conditional-types

[fatcerberus]

On a side note, T0 should be written as

type T0 = (1 | 2 | '3') & number

because & has higher precedence than |.

[NWYLZW]

Working as intended. https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#distributive-conditional-types

Yes, I've seen this. So is this true even in the else branch? Here, this looks very strange.

[fatcerberus]

So is this true even in the else branch?

Yes. Distribution is over the entire conditional type, not individual branches. In other words it runs the ternary conditional expression once for each member of the union and then reassembles it at the end.

This does what you want:

export type Collect0<T, U> = [T] extends [[]] ? never : [T & U]

[NWYLZW]

You are faster than me, haha.

[NWYLZW]

A little weird, but I get it, thanks for your help.