M12 Lifecycle

This is a design layer skill that helps you think through resource lifecycle questions before you write code. It maps patterns like RAII, lazy initialization, and connection pooling to concrete Rust implementations, then shows you which Layer 1 skills handle the actual code. The tables are genuinely useful: they show when Drop fires, how to choose between OnceLock and LazyLock, and why you'd pool versus create per use. It's structured around tracing up to domain constraints and down to implementation details, which matches how you actually think through these decisions. The anti-patterns section is honest about common mistakes like forgetting cleanup or reaching for lazy_static when stdlib works fine.

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last updated: Aug 21, 2026

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Install

$ npx -y skills add actionbook/rust-skills --skill m12-lifecycle --agent claude-code

Installs into .claude/skills of the current project.

Files

Resource Lifecycle

Layer 2: Design Choices

Core Question

When should this resource be created, used, and cleaned up?

Before implementing lifecycle:

What's the resource's scope?
Who owns the cleanup responsibility?
What happens on error?

Lifecycle Pattern → Implementation

Pattern	When	Implementation
RAII	Auto cleanup	`Drop` trait
Lazy init	Deferred creation	`OnceLock`, `LazyLock`
Pool	Reuse expensive resources	`r2d2`, `deadpool`
Guard	Scoped access	`MutexGuard` pattern
Scope	Transaction boundary	Custom struct + Drop

Thinking Prompt

Before designing lifecycle:

What's the resource cost?
- Cheap → create per use
- Expensive → pool or cache
- Global → lazy singleton
What's the scope?
- Function-local → stack allocation
- Request-scoped → passed or extracted
- Application-wide → static or Arc
What about errors?
- Cleanup must happen → Drop
- Cleanup is optional → explicit close
- Cleanup can fail → Result from close