# "consuming" the hash instead of just fetching from it

**URL:** <https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565>\
**Category:** Ruby\
**Created:** [May 22, 2009, 1:10pm UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565 "2009-05-22T13:10:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![balint](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@balint](https://www.ruby-forum.com/u/balint)\
**Post date:** [May 22, 2009, 1:10pm UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565/1 "2009-05-22T13:10:54Z")

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Hi,

Deleting (vs. just fetching) the hash key from an options hash that  
was passed in as an argument to the method seems prevalent. I saw it  
in several high-quality OS projects (e.g DataMapper, Rails)

For example:

unless options.delete(:only\_path)  
url \<\< (options.delete(:protocol) || ‘http’)  
url \<\< ‘://’ unless url.match("://")  
…  
end

I wonder what advantage the above snippet has instead of writing:

unless options[:only\_path]  
url \<\< (options[:protocol] || ‘http’)  
url \<\< ‘://’ unless url.match("://")  
…  
end

Thank you,  
Balint

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<div class="post-metadata">

**Author:** ![balint](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@balint](https://www.ruby-forum.com/u/balint)\
**Post date:** [May 22, 2009, 1:17pm UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565/2 "2009-05-22T13:17:55Z")

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On Fri, May 22, 2009 at 1:10 PM, Balint E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> ```
> url << '://' unless url.match("://")
> 
> ```
> 
> Thank you,  
> Balint

It’s usually a good idea to consume the option if you are receiving  
options that any methods you will subsequently call, won’t need (or  
may break when receiving) them.  
i.e. options specific for the particular method.

If you are not going to pass the options onto other methods, then  
there is nothing wrong with just referencing them.

Andrew T.  
[http://ramblingsonrails.com](http://ramblingsonrails.com)

[http://MyMvelope.com](http://MyMvelope.com) - The SIMPLE way to manage your savings

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<div class="post-metadata">

**Author:** ![balint](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@balint](https://www.ruby-forum.com/u/balint)\
**Post date:** [May 22, 2009, 1:42pm UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565/3 "2009-05-22T13:42:30Z")

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On Fri, May 22, 2009 at 1:10 PM, Balint E. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Hi,
> 
> Deleting (vs. just fetching) the hash key from an options hash that  
> was passed in as an argument to the method seems prevalent.  
> I strongly disagree.  
> I saw it  
> in several high-quality OS projects (e.g DataMapper, Rails)  
> Rails high-quality? On what basis?  
> Please do not take this as a provocation, it is just the first time I  
> have heard this claim (well maybe DHH said something similar once, but  
> do not quote me, please;)
> 
> For example:
> 
> unless options.delete(:only\_path)  
> url \<\< (options.delete(:protocol) || ‘http’)  
> url \<\< ‘://’ unless url.match(“://”)  
> …  
> end
> 
> I wonder what advantage the above snippet has instead of writing:  
> I would say that context is king. If the author of the above snippet  
> deletes values from the hash she has probably a (good) reason.  
> It is not very difficult to imagine some reasons, e.g. checking later  
> for the same values again (but please see below).  
> I would however take another look at the whole setup of the thing, if  
> I were e.g. a code reviewer. This seems not a case I would mute  
> objects a priori, thus I too would be intrigued by the rationale  
> behind this.  
> If you are too, which I have understood from your post, than you might  
> just want to follow the lifetime of options in the code to  
> understand/approve/disapprove about this code.

HTH  
Robert

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<div class="post-metadata">

**Author:** ![balint](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@balint](https://www.ruby-forum.com/u/balint)\
**Post date:** [May 25, 2009, 10:40am UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565/4 "2009-05-25T10:40:11Z")

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2009/5/22 Markus S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > ```
> > url << (options.delete(:protocol) || 'http')
> > 
> > ```
> 
> @b = opts.delete(:b) || “b”  
> raise “unkown options: %s” % opts.keys.inspect unless opts.empty?  
> end

You can have that with the non deletion approach as well.

I agree to what Robert said: this should be carefully inspected.  
Generally I would refrain from changing an argument, especially if it  
is some global options object. These options might be needed in other  
places as well and if they are modified by code other than the option  
parsing (or reading) process then chances are that something will  
break. For example, consider two places in code which need to react  
on the same option value then only one of them gets the value with the  
“delete pattern” and even worse, things may accidentally work  
initially but break if initialization order is changed.

Also, if the options instance is frozen after being filled by option  
parsing or reading process the delete approach won’t work any more.  
As a general rule of thumb it is safer to not modify option arguments.

Kind regards

robert

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<div class="post-metadata">

**Author:** ![balint](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@balint](https://www.ruby-forum.com/u/balint)\
**Post date:** [May 22, 2009, 7:47pm UTC](https://www.ruby-forum.com/t/consuming-the-hash-instead-of-just-fetching-from-it/168565/5 "2009-05-22T19:47:15Z")

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On Fri, May 22, 2009 at 08:10:09PM +0900, Balint E. wrote:

> ```
> url << '://' unless url.match("://")
> ...
> 
> ```
> 
> end

This snippset let you test on “mispelled” or “extra” opts:

Example:

def initialize(opts)  
@a = opts.delete(:a) || raise(“missing :a”)  
@b = opts.delete(:b) || “b”  
raise “unkown options: %s” % opts.keys.inspect unless opts.empty?  
end

> Balint  
> Markus