Day 2 – Go Interfaces and Concurrency

Today's Focus

Explore Go interfaces, concurrency primitives, and Go modules with external dependencies.

Tasks

• Define a Formatter interface with a Format(counts []WordCount) string method. Implement two structs that satisfy it: PlainFormatter (plain text table) and JSONFormatter (JSON output). Your main.go should accept a --format flag and select the right implementation.
• Write a concurrent version of the file reader: use goroutines and a channel to process multiple files in parallel (pass multiple file paths as arguments). Use a sync.WaitGroup to wait for all goroutines to complete before printing results.
• Add an external dependency: go get github.com/spf13/cobra (or github.com/urfave/cli/v2). Refactor your CLI to use it for argument parsing and help text. Run go mod tidy and inspect go.mod and go.sum.
• Understand go.sum: find your new dependency's hash in go.sum. Explain in a comment why go.sum is committed to version control but should never be hand-edited.
• Run go list -m all to see the full dependency graph. Identify a transitive dependency you did not add directly.
• Add go generate support: add a comment //go:generate go fmt ./... and run go generate ./.... Discuss what go generate is typically used for in larger projects.

Reading / Reference

• A Tour of Go — Interfaces and Concurrency sections.
• Go docs: Go Modules Reference — the module file, go.sum, and go mod tidy.
• Go by Example — Goroutines, Channels, WaitGroups, Interfaces.