Packages & Modules — When Gemfile Becomes go.mod

To use external libraries in Ruby: add gem 'rails' to Gemfile and run bundle install.

In Go: run go get github.com/gin-gonic/gin and it's auto-added to go.mod.

Gemfile vs go.mod

Ruby's Gemfile lists gem names with version constraints: gem 'rails', '~> 7.0'
Go's go.mod lists module paths (usually GitHub URLs) with versions: require github.com/gin-gonic/gin v1.9.1

Biggest difference: RubyGems is a central registry where gem install rails works by name alone. Go has no central registry — GitHub URLs are the package identifiers.

require vs import

Ruby: require 'json' — loads by filename or gem name.
Go: import "encoding/json" — imports by package path. Unused imports cause compile errors. Ruby doesn't care if you require something you don't use.

Directory = Package

In Ruby, file structure and module/class structure are loosely connected (Rails autoload handles it). In Go, one directory = one package. All .go files in the same directory must have the same package declaration.

GOPATH → Go Modules

Old Go required all code in a fixed GOPATH directory. Like being forced to develop all projects in ~/ruby_projects/. Now Go Modules (go.mod) lets you work anywhere. The problem Bundler solved — Go solved it in 2019.