如何将字符串插值代码传递到Rails应用模板代码块？

Question

According to Rails Application Templates this is how one can write ruby code into the file:

file 'path/to/my_file.rb', <<-CODE
  class Object
    def not_nil?
      !nil?
    end

    def not_blank?
      !blank?
    end
  end
CODE

However when I try to add code containing string interpolation between <<-CODE and CODE , it fails on its first occurrence.

My file call:

file 'lib/person.rb', <<-CODE
# frozen_string_literal: true

class Person
  def initialize(first_name, last_name)
    @full_name = "#{first_name.capitalize} #{last_name.capitalize}#"
  end
end
CODE

Error message:

template.rb:50:in apply : undefined local variable or method first_name for Rails::Generators::AppGenerator:0x00005557a8d85090 (NameError)

My understanding is that the template generator tries to execute the interpolated code.

What I tried was simply escaping the " double quotes, like:

file 'lib/person.rb', <<-CODE
# frozen_string_literal: true

class Person
  def initialize(first_name, last_name)
    @full_name = \"#{first_name.capitalize} #{last_name.capitalize}#\"
  end
end
CODE

but it did not help, resulting in exactly the same error.

How can I approach this?

Answer 1

You are trying to use heredoc with string interpolation, which obviously fails on the attempt to interpolate first_name . To prevent the heredoc string interpolation, use FOO<<-'CODE' instead:

file 'lib/person.rb', <<-'CODE'
# frozen_string_literal: true

class Person
  def initialize(first_name, last_name)
    @full_name = "#{first_name.capitalize} #{last_name.capitalize}#"
  end
end
CODE