Match/filter strings from string literal union that match criteria

[sage pike]

I have an input type "foo" | "barX" | "batX" and would like to derive a type only contains the string literals ending with X but without X: "bar" | "bat".
I triedts Input extends `${infer A}X` ? A : neverbut as soon as Input contains a single "invalid" value it becomes never.
Playground below.

[cobalt hawk]

Function#5603

Playground Link

Preview:ts ... type Foo = Input extends `${infer A}X` ? A : never ...

[sage pike]

lol i think i found the solution, please let me know if this is the right way or not:ts Input extends `${infer A}.${HTTPCode}` | infer B ? A : neveri literally just added | infer B

[cobalt rampart]

original example would work with generics

type Foo<T> = T extends `${infer A}X` ? A : never

that makes it behave distributively on an union

[sage pike]

thanks a lot! works very nicely :)
i'm curious about the distributive behaviour. is there any documentation on this or an article?

[cobalt rampart]

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

[sage pike]

thanks again :)