# Function lookup in ruby

**URL:** <https://www.ruby-forum.com/t/function-lookup-in-ruby/183000>\
**Category:** Ruby\
**Created:** [February 5, 2010, 7:41pm UTC](https://www.ruby-forum.com/t/function-lookup-in-ruby/183000 "2010-02-05T19:41:51Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![opti900](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/bc8723/32.png) [@opti900](https://www.ruby-forum.com/u/opti900)\
**Post date:** [February 5, 2010, 7:41pm UTC](https://www.ruby-forum.com/t/function-lookup-in-ruby/183000/1 "2010-02-05T19:41:51Z")

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Hi all,  
I was wondering what happened in the background of following snippet.  
First I define a method v1, and I am able to call v1. Then I redefine v1  
as an array; after that I can only call v1 as a function by calling  
v1(). How does ruby look up v1 as a function and variable? Thanks

irb(main):001:0\> def v1  
irb(main):002:1\> puts ‘printing from method v1’  
irb(main):003:1\> end  
=\> nil  
irb(main):004:0\> v1  
printing from method v1  
=\> nil  
irb(main):005:0\> v1 = []  
=\> []  
irb(main):006:0\> v1  
=\> []  
irb(main):007:0\> v1()  
printing from method v1  
=\> nil

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**Author:** ![opti900](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/bc8723/32.png) [@opti900](https://www.ruby-forum.com/u/opti900)\
**Post date:** [February 5, 2010, 8:18pm UTC](https://www.ruby-forum.com/t/function-lookup-in-ruby/183000/2 "2010-02-05T20:18:28Z")

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On Fri, Feb 5, 2010 at 11:42 AM, Cnm C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> irb(main):004:0\> v1  
> printing from method v1  
> =\> nil

At this point, since you ONLY have method/function named ‘v1’ defined,  
the interpreter unambiguously knows you’re making a call to that  
method sans parenthesis.

> irb(main):005:0\> v1 = []  
> =\> []

Now that you’ve ALSO created an Array instance stored in a variable  
named ‘v1’ you can no longer call your function/method the way you did  
before because the two items overlap by name (but both still exist  
independently).

> irb(main):006:0\> v1  
> =\> []

As you noted, the interpreter prefers the variable ‘v1’ over the method.

> irb(main):007:0\> v1()  
> printing from method v1  
> =\> nil

Now that you added parenthesis, the interpreter knows you’re wanting  
to call the method ‘v1’. You could also do:

method(:v1).call

Or:

send(:v1)

Those would also call the method.

How’s THIS for fun:

irb(main):001:0\> def foo  
irb(main):002:1\> puts “This is the method foo()”  
irb(main):003:1\> end  
=\> nil  
irb(main):004:0\> foo  
This is the method foo()  
=\> nil  
irb(main):005:0\> foo = method(:foo)  
=\> #\<Method: Object#foo\>  
irb(main):006:0\> foo  
=\> #\<Method: Object#foo\>  
irb(main):007:0\> foo()  
This is the method foo()  
=\> nil  
irb(main):008:0\> foo.call  
This is the method foo()  
=\> nil

I sure love Ruby!

Aaron out.

Aaron out.

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<div class="post-metadata">

**Author:** ![opti900](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/bc8723/32.png) [@opti900](https://www.ruby-forum.com/u/opti900)\
**Post date:** [February 5, 2010, 8:54pm UTC](https://www.ruby-forum.com/t/function-lookup-in-ruby/183000/3 "2010-02-05T20:54:46Z")

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On Feb 5, 2010, at 1:42 PM, Cnm C. wrote:

> irb(main):004:0\> v1  
> printing from method v1

At this point the only thing named ‘v1’ is a method  
so the method is called.

> =\> nil  
> irb(main):005:0\> v1 = []  
> =\> []

Now there are two things named ‘v1’ a method  
and a local variable. Name resolution prefers  
local variables so…

> irb(main):006:0\> v1  
> =\> []

The local variable is referenced

> irb(main):007:0\> v1()  
> printing from method v1  
> =\> nil

By adding the explicit parens you’ve given Ruby  
a hint that you want to call a method and not  
lookup a local variable.

Alternatively you could do:

self.v1

which would also reference the method and not  
the local variable.

Gary W.

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<div class="post-metadata">

**Author:** ![opti900](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/bc8723/32.png) [@opti900](https://www.ruby-forum.com/u/opti900)\
**Post date:** [February 5, 2010, 9:44pm UTC](https://www.ruby-forum.com/t/function-lookup-in-ruby/183000/4 "2010-02-05T21:44:08Z")

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Thanks Gary and Aaron. I understand it now.  
Gary W. wrote:

> On Feb 5, 2010, at 1:42 PM, Cnm C. wrote: