Now that homebrew/versions has been deprecated, homebrew/core supports multiple versions of formulae with a new naming format.

In homebrew/versions the formula for GCC 6 was named gcc6.rb and began with class Gcc6 < Formula. In homebrew/core this same formula is named gcc@6.rb and begins with class GccAT6 < Formula.

Acceptable versioned formulae

Homebrew’s versions are not intended to be used for any old versions you personally require for your project; formulae submitted should be expected to be used by a large number of people and still supported by their upstream projects.

Versioned formulae we include must meet the following standards:

You should create your own tap for formulae you or your organisation wishes to control the versioning of or those that do not meet the above standards.

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