m02-resource

Smart pointer and resource ownership patterns for Rust heap allocation and reference counting. Layer 1: Language Mechanics What ownership pattern does this resource need? Before choosing a smart pointer, understand: Before choosing a smart pointer: What's the ownership model? What's the thread context? Are there cycles? When pointer choice is unclear, trace to design: From design to implementation: - Guides ownership decisions through a three-step model: single vs. shared ownership, single-threaded vs. multi-threaded context, and presence of reference cycles - Covers six core types (Box, Rc, Arc, Weak, Cell, RefCell) with a decision flowchart and quick reference table for choosing the right pattern - Includes common errors and anti-patterns with fixes, such as using Weak to break cycles, avoiding unnecessary Arc overhead, and preventing RefCell panics - Traces design questions upward to concurrency and mutability concerns, and downward to concrete implementation choices - Is ownership single or shared? - Is access single-threaded or multi-threaded? - Are there potential cycles?