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I'm new to Ruby, but coming up to speed quickly. One question I still
have never seen a good explanation to is this: When is it preferred to a
key a hash with a symbol, and when is it keyed by string? Is this just
personal preference, or is there a rule of thumb?

For example, in the Rails book, the session variable is always populated
with symbols, i.e.:

session[:user] = User.new

It's also obviously completely common throughout the Rails framework
(e.g., :controller =>, :action =>, etc.)

So, when should I use what...or what should I prefer?

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Posted via http://www.ruby-forum.com/.

John Blanco wrote:
> I'm new to Ruby, but coming up to speed quickly. One question I still
> have never seen a good explanation to is this: When is it preferred to a
> key a hash with a symbol, and when is it keyed by string? Is this just
> personal preference, or is there a rule of thumb?
>
> For example, in the Rails book, the session variable is always populated
> with symbols, i.e.:
>
> session[:user] = User.new
>
> It's also obviously completely common throughout the Rails framework
> (e.g., :controller =>, :action =>, etc.)
>
> So, when should I use what...or what should I prefer?

This question comes up a lot. You can search the list archives for
comprehensive discussions. Try
http://groups.google.com/group/comp....95f6051aebe0ae

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Posted via http://www.ruby-forum.com/.

On 5/29/07, John Blanco <> wrote:
> I'm new to Ruby, but coming up to speed quickly. One question I still
> have never seen a good explanation to is this: When is it preferred to a
> key a hash with a symbol, and when is it keyed by string? Is this just
> personal preference, or is there a rule of thumb?
>
> For example, in the Rails book, the session variable is always populated
> with symbols, i.e.:
>
> session[:user] = User.new
>
> It's also obviously completely common throughout the Rails framework
> (e.g., :controller =>, :action =>, etc.)
>
> So, when should I use what...or what should I prefer?

Symbols are ligh-weight, they don't have so much methods to initialize
has strings:

irb(main):009:0> :asd.methods.size
=> 45
irb(main):010:0> "asd".methods.size
=> 143

So thats why you use it in params or other places when you just need
the name. Also a difference is that a symbol :sym is :sym everywhere,
but a string "string" -only the string, not assigned to a variable- is
a different refence to a String object each time you write "string" .

Those are the most important diferences IMO. Sorry if i wasn't that clear tho.

Cheers

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Hi,

One thing to keep in mind is that, as far as I know, symbols are
never garbage collected, so their excessive/inappropriate use might
introduce risk of memory leaks.

George

On 30 May 2007, at 00:06, Dave Grijalva wrote:

> I think the second point that Emilio was making is the more
> important one.
> Let me try to clarify:
>
> irb(main):008:0> puts "foo".object_id
> 1724824
> => nil
> irb(main):009:0> puts "foo".object_id
> 1708744
> => nil
> irb(main):010:0> puts :foo.object_id
> 3678478
> => nil
> irb(main):011:0> puts :foo.object_id
> 3678478
>
>
> You can see here that a new String object is created every time you
> use a
> literal string. With a symbol, however, you are re-using the same
> object
> anywhere you use a symbol with the same name. Using symbols can
> save you a
> lot of resources, both processor time and memory.
>
> -dave
>
> On 5/29/07, Emilio Tagua <> wrote:
>>
>> On 5/29/07, John Blanco <> wrote:
>> > I'm new to Ruby, but coming up to speed quickly. One question I
>> still
>> > have never seen a good explanation to is this: When is it
>> preferred to a
>> > key a hash with a symbol, and when is it keyed by string? Is
>> this just
>> > personal preference, or is there a rule of thumb?
>> >
>> > For example, in the Rails book, the session variable is always
>> populated
>> > with symbols, i.e.:
>> >
>> > session[:user] = User.new
>> >
>> > It's also obviously completely common throughout the Rails
>> framework
>> > (e.g., :controller =>, :action =>, etc.)
>> >
>> > So, when should I use what...or what should I prefer?
>>
>> Symbols are ligh-weight, they don't have so much methods to
>> initialize
>> has strings:
>>
>> irb(main):009:0> :asd.methods.size
>> => 45
>> irb(main):010:0> "asd".methods.size
>> => 143
>>
>> So thats why you use it in params or other places when you just need
>> the name. Also a difference is that a symbol :sym is :sym everywhere,
>> but a string "string" -only the string, not assigned to a
>> variable- is
>> a different refence to a String object each time you write
>> "string" .
>>
>> Those are the most important diferences IMO. Sorry if i wasn't
>> that clear
>> tho.
>>
>> Cheers
>>
>>

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