These are slow because of some Pathname related reasons so it's been
changed up to use `Dir.glob` instead and that makes a large difference.
```
$ hyperfine --parameter-list branch master,speed-up-loading-cask-and-formula-file-names,speed-up-loading-cask-and-formula-file-names_v2 --warmup 5 --setup 'git switch {branch}' 'brew cat gimp'
Benchmark 1: brew cat gimp (branch = master)
Time (mean ± σ): 2.150 s ± 0.014 s [User: 1.369 s, System: 0.745 s]
Range (min … max): 2.126 s … 2.174 s 10 runs
Benchmark 2: brew cat gimp (branch = speed-up-loading-cask-and-formula-file-names)
Time (mean ± σ): 1.814 s ± 0.012 s [User: 1.068 s, System: 0.711 s]
Range (min … max): 1.797 s … 1.840 s 10 runs
Benchmark 3: brew cat gimp (branch = speed-up-loading-cask-and-formula-file-names_v2)
Time (mean ± σ): 1.489 s ± 0.009 s [User: 0.905 s, System: 0.550 s]
Range (min … max): 1.478 s … 1.503 s 10 runs
Summary
brew cat gimp (branch = speed-up-loading-cask-and-formula-file-names_v2) ran
1.22 ± 0.01 times faster than brew cat gimp (branch = speed-up-loading-cask-and-formula-file-names)
1.44 ± 0.01 times faster than brew cat gimp (branch = master)
```
The main class you should look at is the {Formula} class (and classes linked from there). That's the class that's used to create Homebrew formulae (i.e. package descriptions). Assume anything else you stumble upon is private.
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