CricketScript Lesson 10 of 11 · Test, ODI, or T20 | Course

Test, ODI, or T20?

Same shape — innings, overs, runs. Different format.

An innings is an innings. It has a format, a number of overs, a running score. Whether it's a five-day Test, a fifty-over ODI, or a twenty-over T20, the shape is the same. Only the format — that one label that hangs off the top of the scorecard — changes.

Innings<T> says exactly that. The shape is fixed; the format slot is a parameter you fill in. Build an Innings<'Test'>, or an Innings<'T20'>, and TypeScript carries the format around with the data — every place that reads .format knows which one it got.

Pick a format. Watch the same generic interface lock in three different innings shapes.

Pick a format. Innings<T> fills in the rest.

Innings<T>

format —

overs —

score —

One shape, three formats — that's a generic.

<T> is a type parameter — a slot the caller fills in. The interface body uses T the way a function uses an argument. The shape is reusable, the format stays exact.

type Format = 'Test' | 'ODI' | 'T20';

interface Innings<T extends Format> {
  format: T;
  overs:  number;
  score:  { runs: number; wickets: number };
}

const first: Innings<'T20'> = {
  format: 'T20',
  overs:  20,
  score:  { runs: 186, wickets: 4 },
};

Generics keep shapes honest.

You used one Innings<T> interface to build three different innings. The format wasn't a string-typed comment — it was tracked by TypeScript as 'Test', 'ODI', or 'T20' for the lifetime of that value.

Use a generic when the same shape applies to many specific types — a container, a wrapper, a record. The shape becomes a function over types: pass in the type, get back the specific version.

Lesson 11 — All-rounders →