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module Foo
end

Given a module Foo, how do you define a nested module Bar?

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module Foo
    module Bar
    end
end

There’s a number of ways. First, most obvious one is to eval a string.

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module Foo
end

name = 'Bar'

Foo.class_eval <<RUBY
  module #{name}
  end
RUBY

Foo::Bar # => Foo::Bar

While this certainly works and gets job done, it has some flaws. First, it’s a string, so some editors and IDEs will get confused and lose coloring/completion. Second, there’s no validation on module name. In best case, you’ll get compiler error. In worst case, you’ll get hard to track bugs.

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module Foo
end

bar = Module.new
Foo.const_set(:Bar, bar)

Foo::Bar # => Foo::Bar

This one is better. You clearly state that you’re going to set a constant, and module name is pretty restricted.

Are there other ways to do this?