What's the difference between a string and a symbol in Ruby?

Question

What's the difference between a string and a symbol in Ruby and when should I use one over the other?

Answer 1

What are the differences between Symbols and Strings?

1. Symbols are immutable: Their value remains constant.
2. Multiple uses of the same symbol have the same object ID and are the same object compared to string which will be a different object with unique object ID, everytime.
3. You can't call any of the String methods like split on Symbols.

From Understanding Differences Between Symbols & Strings in Ruby

If you know Chinese, you can also read 理解 Ruby Symbol.

Answer 2

The main difference is that multiple symbols representing a single value are identical whereas this is not true with strings. For example:

irb(main):007:0> :test.object_id => 83618 irb(main):008:0> :test.object_id => 83618 irb(main):009:0> :test.object_id => 83618 

Those are three references to the symbol :test, which are all the same object.

irb(main):010:0> "test".object_id => -605770378 irb(main):011:0> "test".object_id => -605779298 irb(main):012:0> "test".object_id => -605784948 

Those are three references to the string "test", but are all different objects.

This means that using symbols can potentially save a good bit of memory depending on the application. It is also faster to compare symbols for equality since they are the same object, comparing identical strings is much slower since the string values need to be compared instead of just the object ids.

As far as when to use which, I usually use strings for almost everything except things like hash keys where I really want a unique identifier, not a string.