Go Packages Rulebook

For reference summary of Go packages.

About a Package

• It’s just a physical directory.
• Lets you organize your code.
• Enables reusability by allowing you to use other packages.
• Helps to enable code encapsulation.
• Represents a single concept.
• Small and many.

Package Rules

Source Files

• All code written in Go belongs to a package.

Package Directory

• Directory names and the package names should be the same.
• All source files in a directory belong to only one package.
• You can’t split a package into more than one directory.
• Packages live inside working space directory named $GOPATH/src.

Identity

• A package can have the same name with another package if they live inside separate directories.

Package Types

• The main package is the entry-point package for executable programs.
• Library packages are only reusable packages and don’t contain main package, and an entry-point (mostly).

Functions and Variables

• In a Go package, there is no such thing as local variables or functions only belong to one source code file.

Importing

• Packages are imported with import keyword. Standard library packages can be imported by its name only (rather than full path). When importing other packages, it’s a good idea to supply the full path.
• For simple programs, you can only have package main. For bigger programs, you may define your own packages.
• Packages are imported only once. You can import the same package in many packages, and, it will be imported only once.

Sub-packaging

• No support.
• You can put packages inside other package’s directories to weakly imitate sub-packaging for the organization.

Alright, that’s all for now. Thank you for reading so far.

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