M05 Type Driven

The m05-type-driven skill teaches developers how to use Rust's type system to prevent invalid states and encode invariants at compile time rather than relying on runtime validation. It covers patterns like newtypes, type state, PhantomData, marker traits, and builders that allow developers to make invalid states unrepresentable. This skill is for Rust engineers building robust systems who need to shift validation logic from runtime checks to compile-time type constraints.

skills.sh installs: 786
GitHub stars: 1.3K
last updated: Jul 14, 2026

View on GitHub

Install

$ npx -y skills add zhanghandong/rust-skills --skill m05-type-driven --agent claude-code

Installs into .claude/skills of the current project.

Files

Type-Driven Design

Layer 1: Language Mechanics

Core Question

How can the type system prevent invalid states?

Before reaching for runtime checks:

Can the compiler catch this error?
Can invalid states be unrepresentable?
Can the type encode the invariant?

Error → Design Question

Pattern	Don't Just Say	Ask Instead
Primitive obsession	"It's just a string"	What does this value represent?
Boolean flags	"Add an is_valid flag"	Can states be types?
Optional everywhere	"Check for None"	Is absence really possible?
Validation at runtime	"Return Err if invalid"	Can we validate at construction?

Thinking Prompt

Before adding runtime validation:

Can the type encode the constraint?
- Numeric range → bounded types or newtypes
- Valid states → type state pattern
- Semantic meaning → newtype
When is validation possible?
- At construction → validated newtype
- At state transition → type state
- Only at runtime → Result with clear error