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

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.

An additional difference between String and Symbol is that a String has a lot more methods on it for string manipulation, while a Symbol is a relatively lean object.

Check out the documentation for the String class and the Symbol class.

Case where symbol can be disaster. Lets say you have params.map(&:to_sym) in your rails controller . Now here if you are converting the data provided by the user to symbol due to some reason then it could be dangerous. If the data provided by the user is too large and as we know that symbol is not a garbage collector, you might end up exhausting your server's memory which can takedown your website.

The main difference is that string can have value inside a variable whereas symbol not . For example:

x     =     "hello"
p x  =>     "hello"
p :x =>     :x

A symbol is something you use to represent names and strings. You would want to use a symbol when you may have need to use a string several times as this far easier and more productive.

And just found this via google, which may offer greater detail: Here you go

Symbols and strings are completely different this post has a little insight into the differences. As to when and where to use them, there is a pretty extensive post on this subject over on has many :through.