The internal Package

The internal package is an access-restriction mechanism that lets certain packages be used only in a limited way. In other words, packages inside an internal directory can only be imported by packages located in that same direct parent folder of internal, or in its subdirectories.

In the example above, the contents of the crypto package can only be imported inside packages defined within the business folder. For example, the crypto package can be used inside http.go, but it can't be used inside server/web.go.

Wherever you want packages to be unusable outside of their parent package, you can put those packages inside an internal folder, as in the example above.

Naming Packages

By following the principles below, we can do a better job naming packages:

• Package names should preferably be short and clear. For example, time, list, and http are good examples of naming.
• Package names should preferably be lowercase and have no underscores. For example, names like priority_queue and mixedCaps don't follow this rule.
• Package names should preferably be abbreviated if the abbreviation is familiar to other developers. For example, strconv (string conversion) and syscall (system call) are good examples of abbreviation.

Modules

In Go, package and module are two important concepts. 

• A package is a collection of go files inside a directory that together provide some functionality.
• A module is a Go project together with a go.mod file, which defines the project's version, dependencies, and path.

Using the go mod init command together with a name, you can create a module:

Running this command creates two files named go.mod and go.sum. In short:

• The go.mod file specifies the module's name, the required Go version, and the project's dependencies.

• The go.sum file contains checksum values for each dependency, as well as the hash of that dependency's go.mod file. This file's main purpose is to keep the program's runs and builds reproducible and secure. Every time we download a dependency, Go compares its hash with the value inside go.sum to make sure the downloaded content is exactly what was previously verified.

Using the go get command, you can install a module as a dependency. For example, running the command below installs the uuid module in the project:

And then you can import and use this module's packages:

If you no longer want to use a dependency, first remove the code that uses that dependency from your project, and then run the go mod tidy command so that dependency is also removed from go.mod and go.sum.

Previous part: Error Handling | Golang basics

Next part: Reflection | Golang basics