How to clearly compare old value with new one?

Question

A common piece of code that I already repeated some times, and never liked it, consists in save a value, do an action, and evaluate the value afterwards. Look at the following example

old_files = project.files
project.some_operation_dealing_with_files
if old_files == project.files
   puts "not changed"
else
   puts "changed"
end

One of the problems on it is that on the first line, when you read old_files = project.files, it is not clear where you want to get. I imagine that if I could eliminate that variable, the code would be better, but I don't know how to achieve this. I'm also, of course, open to suggestions.

TLDR; Is there a way to rewrite the code without the old_file variable?

Answer 1

Make the object aware if the files state changes and provide a query method to test it. Set the did_change status to false at the start of each method that could change the files state.

project.some_operation_with_files
if project.files_did_change?
  puts "Changed"
else
  puts "No change."
end