Data types: Symbol vs String

[Alistair]

Hello,

I'm right at the start of a new project with Mongoid and I'm wondering
if there are any benefits or disadvantages to using Symbol data type
over String, and, what are the differences between them?

Thank you

--
Alistair

[Khaja Minhajuddin]

You should use a Symbol whenever a field can have a value from a finite set of values. e.g. If you are planning to store the "role" of a "user", it could be a symbol ( :admin, :customer, etc, ). FWIW Mongoid stores this as a "string" in mongodb as mongodb doesn't have any special datatype for Symbols. Mongoid transparently converts it from a String to Symbol while loading it and vice versa while saving it. So, it's only a symbol when loaded in your rails/ruby app, that means you get all the advantages of using symbols only in the rails/ruby context. This question on stackoverflow => http://stackoverflow.com/questions/2415780/why-dont-more-projects-use-ruby-symbols-instead-of-strings shows a few advantages of using Symbols.

Regards

Khaja Minhajuddin
http://cosmicvent.com

[Alistair Holt]

Thanks Khaja. It looks like it's mainly down to personal preference. Is there really an advantage to using Symbols over Strings in finite sets of values when you can specify validates_inclusion :something, :in => xxx for both?

--

Alistair

[Khaja Minhajuddin]

I can't think of anything other than the fact that, if we use symbols only one object is created in memory for one symbol, whereas with strings it creates as many objects as the number of times the string is used.

foo = :something

bar = :something

whatever = :something

<== at this point there is just one instance of :something in memory

foo = "chunky"

bar = "chunky"

baz = "chunky"

<== at this point there are 3 instances of "chunky" in memory.

This is how ruby behaves.

Regards
Khaja Minhajuddin
http://cosmicvent.com

[Visnu Pitiyanuvath]

there's also cost involved interning the symbol the first time. a good description of the differences and when to use them is at http://blog.hasmanythrough.com/2008/4/19/symbols-are-not-pretty-strings

[Alistair Holt]

Thanks guys. That's all really interesting :) Using the Symbol data type I guess there is also a slight cost involved in the string-to-symbol (and back again) conversion in Mongoid itself?

--
Alistair

[Khaja Minhajuddin]

In most cases where you would use a C# or Java enum, Symbols are
better than Strings. Can't say for sure what would be better without
knowing what you are using it for.

> > On Thu, Jan 27, 2011 at 9:31 PM, Alistair Holt <alistairh...@gmail.com>wrote:
>
> >> Thanks Khaja. It looks like it's mainly down to personal preference. Is
> >> there really an advantage to using Symbols over Strings in finite sets of
> >> values when you can specify validates_inclusion :something, :in => xxx for
> >> both?
>
> >> --
> >> Alistair
>

> >> On Jan 27, 2011, at 4:44, Khaja Minhajuddin <minhajud...@cosmicvent.com>

> >> wrote:
>
> >> You should use a Symbol whenever a field can have a value from a finite
> >> set of values. e.g. If you are planning to store the "role" of a "user", it
> >> could be a symbol ( :admin, :customer, etc, ). FWIW Mongoid stores this as a
> >> "string" in mongodb as mongodb doesn't have any special datatype for
> >> Symbols. Mongoid transparently converts it from a String to Symbol while
> >> loading it and vice versa while saving it. So, it's only a symbol when
> >> loaded in your rails/ruby app, that means you get all the advantages of
> >> using symbols only in the rails/ruby context. This question on stackoverflow

> >> => <http://stackoverflow.com/questions/2415780/why-dont-more-projects-use...>
> >>http://stackoverflow.com/questions/2415780/why-dont-more-projects-use...shows

> >> a few advantages of using Symbols.
>
> >> Regards
> >> Khaja Minhajuddin

> >> <http://cosmicvent.com/>http://cosmicvent.com

[iEmpire]

Which is better for the "gender" field: Symbol or String?

[Alistair]

Perhaps a boolean would be more suitable for a field with only two states like a gender field. i.e. male => true

[Nick Hoffman]

On Wednesday, February 23, 2011 4:09:51 AM UTC-5, iEmpire wrote:

Which is better for the "gender" field: Symbol or String?

Mongoid stores symbols as strings in MongoDB, so it boils down to whether symbols or strings suits your application better.

[Kieran P]

The devs of Diaspora would disagree with you there ;-)

http://twitter.com/#!/sarahmei/statuses/8407288230453248