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

Versioned formulae we include in homebrew/core must meet the following standards:

Homebrew’s versions are not intended to be used for any old versions you personally require for your project. You should create your own tap for formulae you or your organisation wish to control the versioning of or those that do not meet the above standards. Software that has regular API or ABI breaking releases still needs to meet all the above requirements; that a brew upgrade has broken something for you is not an argument for us to add and maintain a formula for you.

If there is a formula that currently exists in the Homebrew/homebrew-core repository or has existed in the past (i.e. was migrated or deleted), you can recover it for your own use with the brew extract command. This will copy the desired version of the formula into a custom tap. For example, if your project depends on automake 1.12 instead of the most recent version, you can obtain the automake formula at version 1.12 by running brew extract automake <YOUR_GITHUB_USER>/<YOUR_TAP_REPOSITORY_NAME> --version=1.12. Formulae obtained this way may contain deprecated, disabled or removed Homebrew syntax (e.g. checksums may be sha1 instead of sha256); the brew extract command does not edit or update formulae to meet current standards and style requirements.

We may temporarily add versioned formulae for our own needs that do not meet these standards in homebrew/core. The presence of a versioned formula there does not imply it will be maintained indefinitely or that we are willing to accept any more versions that do not meet the requirements above.

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