Inferring the type of route params from a route path string: An exercise in what template literal types can do (https://www.typescriptlang.org/play?#code/C4TwDgpgBACghsAFgZQgcwLYQHbAM4A88SUEAHsDgCZ5R7ABOAltmgDRSqY75QC8UbBABuEBgD5+sBIlIVqtAAYASAN4sAZmM7osuAL4B6NZu0AlCPX2KoAfmlIue-AQv0OTnrQA+O7rkkALj9nHwdEAG4AKFBIaQY4DE9cQmQ5SmwaOkYWNEkBNPIMrMVAk2…

routes.ts

type PathSegments<Path extends string, Segments = never> = Path extends `${infer Segment}/${infer Rest}` ? PathSegments<Rest, Segments | Segment> : Segments | Path;
type ParamSegments<S extends string> = S extends `:${infer P}` ? P : never;

let segments: PathSegments<'/posts/:id/comments/:comment_id'>;

interface Routes {
    match<Path extends string>(path: Path, cb: (params: Record<ParamSegments<PathSegments<Path>>, string>) => void): void;
}

declare const routes: Routes

routes.match('/posts/:id/comments/:comment_id', (params) => {
    console.log({params})
});