Internal Packages in Go

Go's rigid package visibility rules aim to keep API surfaces well-defined and distinct. However, it's not possible to encapsulate implementation details within smaller packages without exposing them to external consumers when the project grows.

One solution to this dilemma was proposed in Go 1.4: introduce "internal" packages.

Importing Internal Packages

An "internal" package can only be imported by other packages within the same tree. This rule was intended to create a clear separation between public and internal packages, preventing the accidental exposure of internal implementation details.

Example

Attempting to import an internal package from outside its parent tree results in an error:

import (
    "runtime/internal/atomic"
    "runtime/internal/sys"
)

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Error:
imports runtime/internal/atomic: use of internal package not allowed

Can You Access Internal Functions?

The question of using internal functions in a main package arises from the desire to keep implementation details isolated. Unfortunately, this is not an intended use case for internal packages.

The Takeaway

Encapsulating implementation details within internal packages is not practical in Go. Instead, consider refactoring your codebase into distinct modules with well-defined public interfaces. This approach aligns with Go's emphasis on clear API boundaries and promotes code maintainability and extensibility.

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