libr0
Building Rust's Standard Library from Scratch
Learn by building. Understand Rust's core types by implementing them yourself, from simple enums to async runtime internals.
Learn by Building
libr0 takes you through Rust's fundamental types from scratch. Each chapter builds on the previous one, showing you exactly how Option, Box, Vec, Rc, and more work under the hood.
Option
The simplest enum. Pattern matching with Some(T) and None.
Result
Error handling with Ok(T) and Err(E). The ? operator.
Box
First heap allocation. Stack vs heap, Deref trait.
Vec
Growable arrays. Why String is just Vec<u8>.
Cell
Interior mutability with UnsafeCell under the hood.
RefCell
Runtime borrow checking with guard types.
Rc
Reference counting for shared ownership.
Rc + RefCell
Shared mutable state. Build graphs and trees.
What Makes libr0 Different?
De-abstract the Abstractions
Box? Just alloc + dealloc in a struct. RefCell? Just a counter and panic! We show you exactly how it works.
Show the Memory
What's in memory? Show the layout. What does the CPU do? Explain the instruction.
Working Code
Every concept has runnable examples. Understanding comes from code, not theory.
Address Confusion
We call out common misunderstandings explicitly with clear explanations.