String interpolation not working for Ruby heredoc constant

Question

I have a very long constant definition that requires interpolation (the real one is much longer):

const = "This::Is::ThePath::To::MyModule::#{a_variable}".constantize

Now, in order to make it more readable I tried to use heredocs to create a multiline string:

const = <<-EOT.constantize
  This::Is::ThePath::
  To::MyModule::#{a_variable}
EOT

But when I execute it I get a NameError: wrong constant name. Since the first example is working, I assume that it is related to the String interpolation?

Any thoughts on where this is going wrong?

Answer 1

Strip All Whitespace and Newlines from Here-Document

You need to remove all spaces, tabs, and newlines from your interpolated here-document before you invoke #constantize. The following self-contained example will work:

require 'active_support/inflector'

module This
  module Is
    module ThePath
      module To
        module MyModule
          module Foo
          end
        end
      end
    end
  end
end

a_variable = 'Foo'
const = <<EOT.gsub(/\s+/, '').constantize
  This::Is::ThePath::
  To::MyModule::#{a_variable}
EOT

#=> This::Is::ThePath::To::MyModule::Foo

Answer 2

instead:

const = <<-EOT.constantize
  This::Is::ThePath::
  To::MyModule::#{a_variable}
EOT

use:

const = <<-EOT.gsub(/\n/, '').constantize
  This::Is::ThePath::
  To::MyModule::#{a_variable}
EOT

This method that create string <<-EOF ... EOF put \n on the end of line, then constantize can't work properly. Removed undesired character \n, \t, \s and all should work.

Look my test case:

conts = <<-EOF.constantize
=> ActionDispatch::Integration::Session
=> EOF

#> NameError: wrong constant name "Session\n"

conts = <<-EOF.chomp.constantize
=> ActionDispatch::Integration::Session
=> EOF
#> ActionDispatch::Integration::Session

For many lines:

conts = <<-EOF
=> ActionDispatch::
=> Integration::
=> Session
=> EOF
=> "ActionDispatch::\nIntegration::\nSession\n"

Fix it:

conts = <<-EOF.gsub(/\n/, '').constantize
=> ActionDispatch::
=> Integration::
=> Session
=> EOF
=> ActionDispatch::Integration::Session