You can pull in pre-existing modules (we’ll show you how soon!), but you can also make your own. Modules are super easy to make! You just use the module keyword, like so:

module ModuleName # Bits 'n pieces end

Like class names, module names are written in CapitalizedCamelCase, rather than lowercase_with_underscores.

It doesn’t make sense to include variables in modules, since variables (by definition) change (or vary). Constants, however, are supposed to always stay the same, so including helpful constants in modules is a great idea.

Ruby doesn’t make you keep the same value for a constant once it’s initialized, but it will warn you if you try to change it. Ruby constants are written in ALL_CAPS and are separated with underscores if there’s more than one word.

An example of a Ruby constant is PI, which lives in the Math module and is approximately equal to 3.141592653589793. We created our own PI in the previous exercise, but don’t worry: because they’re in separate modules, Ruby knows to keep them separate.



Create your own module called MyLibrary in the editor to the right. Include a constant called FAVE_BOOK and set it equal to a string naming your favorite book!

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