Mapping Data Structures to Borsh — Forge College

How do your Rust structs and enums actually become bytes on Solana? Understanding how Borsh maps data shapes to a wire layout is essential for safe, predictable on-chain storage and future upgrades. What you'll learn: This lesson shows exactly how common Rust types are serialized with Borsh and how those encodings affect offsets, sizing, and upgradeability. You'll see that primitive numeric types are little-endian fixed-size values, while String and Vec of T use a u32 length prefix followed by raw bytes. Learn how Option of T is represented with a presence discriminant and how enums are encoded with a variant index (commonly a u32) followed by the variant payload. We'll walk through examples that let you predict serialized byte size for a struct, identify which fields introduce variable length, and apply practical layout decisions to minimize rent and reallocation friction on Solana. Who this is for: Intermediate Solana/Rust developers who already know basic Rust types and the Borsh encoding rules and now want to design robust on-chain account layouts and migration strategies. Key topics covered: - Borsh field ordering and how declaration order determines byte offsets - Primitive encodings (u8, u64, bool) and little-endian representation - String and Vec of T: u32 length prefixes and variable-size implications - Option of T encoding and when to prefer separate accounts vs Option - Enum discriminants, stable variant ordering, and compatibility concerns - Best practices for field ordering, upgrade patterns, and rent cost reduction Ready to put this into practice? Learn more and continue your Web3 education at https://www.forge.college/