Design Patterns

This is a focused collection of Rust patterns for RTK's CLI filter architecture. It covers seven patterns with real examples: Newtype for type safety (preventing token count mixups), Builder for complex configs, State Machine for parsing multi-section output like pytest results, and others. The guide includes an honest anti-patterns section that pushes back against over-engineering, like adding async traits for "future-proofing" in a deliberately single-threaded tool. The pattern selection table is genuinely useful for deciding when to use what. Use this when you're adding a new filter module or refactoring existing ones and want to avoid both primitive obsession and unnecessary abstraction.

skills.sh installs: 1.9K
GitHub stars: 86K
last updated: Aug 21, 2026

View on GitHub

Install

$ npx -y skills add rtk-ai/rtk --skill design-patterns --agent claude-code

Installs into .claude/skills of the current project.

Files

RTK Rust Design Patterns

Patterns that apply to RTK's filter module architecture. Focused on CLI tool patterns, not web/service patterns.

Pattern 1: Newtype (Type Safety)

Use when: wrapping primitive types to prevent misuse (command names, paths, token counts).

// Without Newtype — easy to mix up
fn track(input_tokens: usize, output_tokens: usize) { ... }
track(output_tokens, input_tokens);  // Silent bug!

// With Newtype — compile error on swap
pub struct InputTokens(pub usize);
pub struct OutputTokens(pub usize);
fn track(input: InputTokens, output: OutputTokens) { ... }
track(OutputTokens(100), InputTokens(400));  // Compile error ✅

// Practical RTK example: command name validation
pub struct CommandName(String);
impl CommandName {
    pub fn new(s: &str) -> Result<Self> {
        if s.contains(';') || s.contains('|') || s.contains('`') {
            anyhow::bail!("Invalid command name: shell metacharacters");
        }
        Ok(Self(s.to_string()))
    }
    pub fn as_str(&self) -> &str { &self.0 }
}