Book: The TypeScript Type System — From Generics to DSL-Level Types

Also by me: The TypeScript Library — the 5-book collection

My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools

Me: xgabriel.com | GitHub

The handbook teaches infer with two examples. Awaited<T> peels a Promise . ReturnType<T> peels a function. Both are linear: one extends , one infer , one shape out. Real codebases ask infer to walk tuples or parse strings, and the working versions usually live in Stack Overflow answers older than the codebase you paste them into.

Five recipes that go past the obvious. Each one starts with a real failure mode and ends with a lesson about how the type system handles distributivity, variance, and recursion depth.

Recipe 1: Last element of a tuple

The wrong version looks right at first glance.

type Last < T extends readonly unknown [] > = T extends readonly [... unknown [], infer L ] ?…