When changing the $LOAD_PATH, why do you use unshift instead of push?

Question

I find ruby load path is an array, and many projects use it like this:

 $:.unshift(File.expand_path("../../lib", __FILE__))

It can add local files to the front of ruby path array to enable us require or load.

So, I hope to know why don't we use push to add the file at the end of the array?

Answer 1

Let's assume you have a "date.rb" file (why not) and you want to load this file, and not the standard library date.

If you use append, your file will never be loaded when you call require 'date' because it's located at the end of the array and the standard date will be found before.

Therefore, if you prepend your path to the load path, you don't risk priority lookup