Difference between various variables scopes in ruby

by

  1. Class variables are the same for all instances, because they’re class variables–associated with the class. Everything access the same variable, including each instance.

  2. No. Local variables are just that–local. They may be local to a function, or local to the class declaration, which is different than being a class variable. Locals in a class declaration go out of scope when the class declaration ends.

  3. That’s because they’re exactly the same–they’re global. Global state is always evil; this is not a property of the language or environment. That said, some global state may be required–that’s just the way it is. It makes sense to use global state when there’s global state. The trick is to use global state properly, which is sometimes a non-trivial endeavor.

  4. That’s just how Ruby is.

  5. One has already been given by Chris.

  6. I would think this question would be largely self-answering. Global when the entire world needs access. Instance when it’s specific to a class instance. Local when it’s only required in a local scope (e.g., a method, a block (note differences between 1.8 and 1.9 with regard to block scope), etc.) Constant when the variable isn’t supposed to change. A class variable when it’s something that either every instance needs, or if exposed via a class method, something tightly associated with a class.

  7. There is no “most use-cases”, it totally depends on what you’re doing with the variable. And public isn’t the de facto choice in Java–it depends on the entity in question. Default Java scope is package-private (methods, properties). Which to use in Ruby depends entirely upon the use-case, noting that as with Java, and even more easily in Ruby, things can be circumvented.

More Related Contents:

  1. How can I access a variable defined in a Ruby file I required in IRB?
  2. What does map(&:name) mean in Ruby?
  3. What does ||= (or-equals) mean in Ruby?
  4. How to sort an array in descending order in Ruby
  5. What does !! mean in ruby?
  6. How to Uninstall RVM? [duplicate]
  7. Difference between DateTime and Time in Ruby
  8. How does the magic comment ( # Encoding: utf-8 ) in ruby​​ work?
  9. sqlite3-ruby install error on Ubuntu
  10. Need a simple explanation of the inject method
  11. DRY Ruby Initialization with Hash Argument
  12. Exporting an Environment Variable in Ruby
  13. ruby inheritance vs mixins
  14. Understanding the “||” OR operator in If conditionals in Ruby
  15. How do I temporarily redirect stderr in Ruby?
  16. Confusion with Atomic Grouping – how it differs from the Grouping in regular expression of Ruby?
  17. Extract number from string in Ruby
  18. Is there a way to remove the BOM from a UTF-8 encoded file?
  19. Using layouts in HAML files independently of Rails
  20. How to implement a short URL like the URLs in Twitter?
  21. How to run untrusted Ruby code inside a safe sandbox?
  22. ‘||=’ operator in Ruby
  23. What does the equal (‘=’) symbol do when put after the method name in a method definition?
  24. Why does “compass watch” say it cannot load sass/script/node (LoadError)?
  25. When to use `require`, `load` or `autoload` in Ruby?
  26. How can I get the absolute URL when extracting links using Nokogiri?
  27. In Ruby why won’t `foo = true unless defined?(foo)` make the assignment?
  28. How to determine if a character is a Chinese character
  29. What does the unary question mark (?) operator do?
  30. Should I use alias or alias_method?

Leave a Comment