May 23
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Want to extend a Solana program safely without breaking existing clients? This lesson walks you step-by-step through adding program logic that consumes new inputs, mutates state, and remains compatible with existing client contracts. What you'll learn In this hands-on lesson you will implement a concrete instruction (ApplyMultiplier) that reads a numeric value from a program account, multiplies it by a multiplier parameter (previously exposed by the client), writes the result back to state, and emits a simple log event. You will locate where the template routes instructions, add a new enum variant, and insert a safe handler in the processor/handler match without destabilizing other flows. The lesson covers state and account access patterns, small refactors to keep logic organized, and unit tests that validate compilation and behavior. Finally you will run a local client invocation against a local validator to demonstrate end-to-end behavior. Who this is for Intermediate Rust and Solana developers who already understand basic program structure, instruction enums, and account serialization. Prior familiarity with running cargo test and a local Solana validator is assumed. Key topics covered - Adding the ApplyMultiplier instruction variant to the instruction enum - Implementing a processor/handler that consumes the multiplier and mutates on-chain state - Preserving client-interaction contracts and account deserialization compatibility - Refactoring small template modules to organize new logic safely - Writing and running unit tests that cover the new instruction - Performing a local client call against a validator to validate end-to-end behavior Ready to continue building with guided lessons and exercises? Visit https://www.forge.college/