# Where to use colon (:) and where to not use it?

**URL:** <https://www.ruby-forum.com/t/where-to-use-colon-and-where-to-not-use-it/211694>\
**Category:** Rails\
**Created:** [September 11, 2011, 9:47am UTC](https://www.ruby-forum.com/t/where-to-use-colon-and-where-to-not-use-it/211694 "2011-09-11T09:47:55Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![luislavena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/0ea827/32.png) [@luislavena](https://www.ruby-forum.com/u/luislavena)\
**Post date:** [September 11, 2011, 9:47am UTC](https://www.ruby-forum.com/t/where-to-use-colon-and-where-to-not-use-it/211694/1 "2011-09-11T09:47:55Z")

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Hi,  
I am a bit confused with ruby syntax with colon. You see  
in controller “render :nothing =\> true”  
and in routes " resources :books"  
and in model “validates :name, :presence =\> true:”

everywhere so is that a key value pair or something else?

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**Author:** ![venkata\_reddy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/b19c9b/32.png) [@venkata\_reddy](https://www.ruby-forum.com/u/venkata_reddy)\
**Post date:** [September 11, 2011, 10:50am UTC](https://www.ruby-forum.com/t/where-to-use-colon-and-where-to-not-use-it/211694/2 "2011-09-11T10:50:59Z")

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@venkata: Ruby makes a lot of things optional that other languages  
require. It makes typing easier, but can lead to the very confusion you  
encountered.

The first shorthand to know is that in Ruby, function and method calls  
can omit the parentheses that bracket the arguments, so your examples:

render :nothing =\> true  
resources :books  
validates :name, :presence =\> true

are actually:

render(:nothing =\> true)  
resources(:books)  
validates(:name, :presence =\> true)

The second shorthand to remember is that in Ruby, if the last argument  
to a function or method is a hash table, you can omit the enclosing {  
}. So the examples are actually:

render({:nothing =\> true})  
resources(:books)  
validates(:name, {:presence =\> true})

And finally, any token that starts with a colon is a “symbol” – it acts  
like a constant string. Symbols are especially useful as keywords,  
which is why they’re often used as the key of a key/value pair in a hash  
table.

So to describe each of your examples:

- render is called with a hash table as its argument. the hash table  
has a single key/value pair where the key is :nothing and the value is  
true.

- resources is called with a single keyword argument

- validates is called with a keyword (:name) as its first argument and  
a hash table as its second argument. the hash table has a single  
key/value pair where the key is :presence and the value is true.

Hope this helps!

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<div class="post-metadata">

**Author:** ![venkata\_reddy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/b19c9b/32.png) [@venkata\_reddy](https://www.ruby-forum.com/u/venkata_reddy)\
**Post date:** [September 11, 2011, 1:04pm UTC](https://www.ruby-forum.com/t/where-to-use-colon-and-where-to-not-use-it/211694/3 "2011-09-11T13:04:30Z")

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Very good explanation! Thank you very much…