class RuboCop::Cop::Rails::IndexBy

}]
[1, 2, 3].map { |el| [foo(el), el] }.to_h
[1, 2, 3].to_h { |el| [foo(el), el] }
[1, 2, 3].each_with_object({}) { |el, h| h = el }
# bad
@example
Rails provides the ‘index_by` method for this purpose.
an enumerable into a hash where the values are the original elements.
`map { … }.to_h`, and `Hash[map { … }]` that are transforming
Looks for uses of `each_with_object({}) { … }`,