# Whats the ruby way of associating metadata with a function

**URL:** <https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043>\
**Category:** Ruby\
**Created:** [November 13, 2007, 9:43am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043 "2007-11-13T09:43:43Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 9:43am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/1 "2007-11-13T09:43:43Z")

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Hi All,

I’ve pretty new to ruby and still getting to know how ruby works. I want  
to associate some metadata to a function. I saw a similar post down this  
line but didn’t get the real answer.

In javascript I’m used to associating metadata with a function as  
follows.

foo.bar = “foobar”;  
function foo(){  
}

Whats the normal ruby practice to do this kind of a thing. Whats the  
ruby way of doing this.

Your help is very much appreciated.

Thanks,  
Keith.

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**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 10:13am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/2 "2007-11-13T10:13:15Z")

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2007/11/13, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> function foo(){  
> }
> 
> Whats the normal ruby practice to do this kind of a thing. Whats the  
> ruby way of doing this.

You typically use a class instance variable. For example:

class Foo  
def self.meta() @method\_meta ||= {} end

def bar() 1 end

meta[:bar]=567  
puts meta[:bar], meta[:foo]  
end

puts Foo.meta[:bar], Foo.meta[:foo]

Kind regards

robert

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<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 10:43am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/3 "2007-11-13T10:43:54Z")

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Hi Robert,

If I extend my question a bit further

foo.bar = “bar”;  
function foo(){  
}

foobar.bar = “foobar”;  
function foobar(){  
}

How can I support something like this?

Thanks,  
Keith.

Robert K. wrote:

> 2007/11/13, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):
> 
> > function foo(){  
> > }
> > 
> > Whats the normal ruby practice to do this kind of a thing. Whats the  
> > ruby way of doing this.
> 
> You typically use a class instance variable. For example:
> 
> class Foo  
> def self.meta() @method\_meta ||= {} end
> 
> def bar() 1 end
> 
> meta[:bar]=567  
> puts meta[:bar], meta[:foo]  
> end
> 
> puts Foo.meta[:bar], Foo.meta[:foo]
> 
> Kind regards
> 
> robert

---

<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 11:20am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/4 "2007-11-13T11:20:33Z")

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On Nov 13, 4:43 am, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> How can I support something like this?

require ‘ostruct’

class FunctionWithMetaData \< OpenStruct  
def initialize(&block)  
super  
@func = block  
end

def call(\*args)  
@func.call(\*args)  
end  
end

foo = FunctionWithMetaData.new { |x|  
x\*10  
}

foo.bar = “qux”  
foo.baz = “bop”

puts foo.bar # =\> “qux”  
puts foo.baz # =\> “bop”  
puts foo.call(3) # =\> 30

fred = FunctionWithMetaData.new {  
“fred function”  
}

fred.arms = 2  
fred.fingers = 10

puts fred.arms # =\> 2  
puts fred.fingers # =\> 10  
puts fred.call # =\> “fred function”

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<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 11:28am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/5 "2007-11-13T11:28:09Z")

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2007/11/13, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> }
> 
> How can I support something like this?

The example is kind of artificial. Can you disclose more detail on  
what you are trying to achieve? There are millions of ways to answer  
your question and meta data for methods might not even be the best  
solution.

Kind regards

robert

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<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 13, 2007, 10:46am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/6 "2007-11-13T10:46:01Z")

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On Nov 13, 3:43 am, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> ruby way of doing this.  
> Three options come to mind:

==================================================  
#1 : add accessors to the singleton of a lambda

foo = lambda {  
puts “foo!!”  
}

class \<\< foo  
attr\_accessor :bar  
end

foo.bar = “foobar”

foo.call # =\> “foo!!”  
puts foo.bar # =\> “foobar”

==================================================  
#2 : add a hash to the singleton of a lambda

foo = lambda {  
puts “foo!!”  
}

class \<\< foo  
def meta  
@meta ||= Hash.new  
end  
end

foo.meta[:bar] = “foobar”

foo.call # =\> “foo!!”  
puts foo.meta[:bar] # =\> “foobar”

==================================================  
#3 : add a method to the singleton of an OpenStruct

require ‘ostruct’

foo = OpenStruct.new

class \<\< foo  
def call  
puts “foo!!”  
end  
end

foo.bar = “foobar”

foo.call # =\> “foo!!”  
puts foo.bar # =\> “foobar”

All other things being equal, I would be inclined toward #3.

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<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 15, 2007, 7:30am UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/7 "2007-11-15T07:30:33Z")

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Hi Robert and others,

We are trying to define a way of writing web services in ruby (Code  
First approach). And we expect to keep it as simple as possible. In  
order to do this we need to define some metadata that we can use to  
generate a pleasant WSDL. This metadata may include things like  
documentation and details about input and output Types. Note that ruby  
is a Dynamic language whereas xml schema is not. And although a  
parameter taken into a function could be of anyType in most cases it  
operates on it assuming its of a certain type. And getting this  
information into the WSDL matters in that case.

Assume that I have a function as follows,

def foo(bar, foobar)

end

I need to get the information on the types expected by this function  
across to the WSDL. I basically need a way to say that bar is a String  
and foobar is an integer. This is where the matadata that I’m talking  
about comes into play.

It will be nice if the Ruby community can help us figure out a nice  
rubish way of doing this. The most important thing is that I want this  
all to fit in with ruby people so this should look rubish as much as  
possible.

Once we get this done we have more cool stuff in mind…

Thanks,  
Keith.

Robert K. wrote:

> 2007/11/13, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):
> 
> > }
> > 
> > How can I support something like this?
> 
> The example is kind of artificial. Can you disclose more detail on  
> what you are trying to achieve? There are millions of ways to answer  
> your question and meta data for methods might not even be the best  
> solution.
> 
> Kind regards
> 
> robert

---

<div class="post-metadata">

**Author:** ![keith](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f05b48/32.png) [@keith](https://www.ruby-forum.com/u/keith)\
**Post date:** [November 15, 2007, 4:13pm UTC](https://www.ruby-forum.com/t/whats-the-ruby-way-of-associating-metadata-with-a-function/120043/8 "2007-11-15T16:13:34Z")

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2007/11/15, Keith C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> information into the WSDL matters in that case.  
> about comes into play.
> 
> It will be nice if the Ruby community can help us figure out a nice  
> rubish way of doing this. The most important thing is that I want this  
> all to fit in with ruby people so this should look rubish as much as  
> possible.

Well, then it sounds as if you need structured data for a method.  
Extending my last proposed solution a bit you could do this:

16:08:14 /cygdrive/c$ cat meta.rb  
require ‘ostruct’

class Foo  
def self.meta()  
@method\_meta ||= Hash.new {|h,k| h[k]=OpenStruct.new}  
end

def bar() 1 end

meta[:bar].length=567  
meta[:bar].return\_type=Integer  
end

puts Foo.meta[:bar]  
16:08:48 /cygdrive/c$ ruby meta.rb  
#  
16:08:50 /cygdrive/c$

Of course you can use a Hash instead of the OpenStruct - but that’s  
probably rather a matter of taste. If you need automatic discovery of  
meta data set I’d probably rather use a Hash - if you know which meta  
data you expect I’d probably use an OpenStruct or a Struct.

Cheers

robert