[ruby-core:71380] [Ruby trunk - Feature #11643] A new method on Hash to grab values out of nested hashes, failing gracefully

[keithrbennett@gmail.com]

Issue #11643 has been updated by Keith Bennett.


I like the 'dig' method approach for these reasons:

* it does not require any fanciness or magic that could confuse novice Rubyists
* it does not require any change to the interpreter
* the name 'dig' is concise and intention-revealing

I have been hoping for this feature for a long time.  This would be great.


Austin Ziegler wrote:
> The problem with `hash.fetch_in(:order, :shipping_info, :country, 'Not
>  found')` is that `'Not found'` is a (possibly) valid key. You would need to
>  implement this with a kwarg.
>  
>  ```ruby
>  class Hash
>  def fetch_in(*keys, **kwargs, &block)
>  keys = keys.dup
>  ckey = keys.shift
>  
>  unless self.key?(ckey)
>  return kwargs[:default] if kwargs.key?(:default)
>  return block.call(ckey) if block
>  fail KeyError, "key not found #{ckey.inspect}"
>  end
>  
>  child = self[ckey]
>  
>  if keys.empty?
>  child
>  elsif child.respond_to?(:fetch_in)
>  child.fetch_in(*keys, **kwargs, &block)
>  else
>  fail ArgumentError, 'more keys than Hashes'
>  end
>  end
>  end
>  
>  a = {
>  a: {
>  b: {
>  c: :d
>  }
>  }
>  }
>  
>  def y
>  yield
>  rescue => e
>  e
>  end
>  
>  p y { a }
>  p y { a.fetch_in(:a) }
>  p y { a.fetch_in(:a, :b) }
>  p y { a.fetch_in(:a, :b, :c) }
>  p y { a.fetch_in(:a, :b, :c, :d) }
>  p y { a.fetch_in(:a, :b, :d) }
>  p y { a.fetch_in(:a, :b, :d, default: 'z') }
>  p y { a.fetch_in(:a, :b, :d) { 'z' } }
>  ```
>  
>  As a proposed name, I suggest `locate`.
>  
>  On Tue, Nov 3, 2015 at 7:03 PM, <dsisnero@gmail.com> wrote:
>  
>  > Issue #11643 has been updated by Dominic Sisneros.
>  >
>  >
>  > Yukihiro Matsumoto wrote:
>  > > I prefer method way to (already reverted)
>  > `params.?[:order].?[:shipping_info].?[:country]`.
>  > > I am not sure `dig` is the best name for it. It's short, concise thought.
>  > > Any other idea, anyone?
>  > >
>  > > Matz.
>  >
>  > clojure has get-in for their maps, how about fetch_in with replacement
>  > like fetch
>  >
>  > hash.fetch_in(:order, :shipping_info, :country, 'Not found')
>  >
>  >
>  > ----------------------------------------
>  > Feature #11643: A new method on Hash to grab values out of nested hashes,
>  > failing gracefully
>  > https://bugs.ruby-lang.org/issues/11643#change-54698
>  >
>  > * Author: Gabe Kopley
>  > * Status: Open
>  > * Priority: Normal
>  > * Assignee:
>  > ----------------------------------------
>  > (I posted this to the mailing list last year [0] and received no response,
>  > but am inspired to file an issue here based on the positive reception to
>  > https://bugs.ruby-lang.org/issues/11537 )
>  >
>  > This comes up sometimes in Rails programming [1]:
>  >
>  > `params[:order] && params[:order][:shipping_info] &&
>  > params[:order][:shipping_info][:country]`
>  >
>  > or
>  >
>  > `params[:order][:shipping_info][:country] rescue nil`
>  >
>  > or
>  >
>  > `params.fetch(:order, {}).fetch(:shipping_info, {}).fetch(:country, nil)`
>  >
>  > What if Hash gave us a method to accomplish this more concisely and
>  > semantically?
>  >
>  > Eg.
>  >
>  > `params.traverse_nested_hashes_and_return_nil_if_a_key_isnt_found(:order,
>  > :shipping_info, :country)`
>  >
>  > Or to take a nice method name suggestion [2]:
>  >
>  > `params.dig(:order, :shipping_info, :country)`
>  >
>  > Another example solution is https://github.com/intridea/hashie#deepfetch
>  > (Although I don't like "fetch" in this method name since it doesn't and
>  > can't take a default value as an argument like Hash#fetch does)
>  >
>  > What do you all think?
>  >
>  >
>  > [0] https://groups.google.com/forum/#!topic/ruby-core-google/guleNgEJWcM
>  >
>  > [1]
>  > https://groups.google.com/d/msg/rubyonrails-core/bOkvcvS3t_A/QXLEXwt9ivAJ
>  >
>  > https://stackoverflow.com/questions/1820451/ruby-style-how-to-check-whether-a-nested-hash-element-exists
>  >
>  > https://stackoverflow.com/questions/19115838/how-do-i-use-the-fetch-method-for-nested-hash
>  >
>  > https://stackoverflow.com/questions/10130726/ruby-access-multidimensional-hash-and-avoid-access-nil-object
>  >
>  > [2] http://stackoverflow.com/a/1820492/283398
>  >
>  >
>  >
>  > --
>  > https://bugs.ruby-lang.org/
>  >
>  
>  
>  
>  -- 
>  Austin Ziegler • halostatue@gmail.com • austin@halostatue.ca
>  http://www.halostatue.ca/ • http://twitter.com/halostatue



----------------------------------------
Feature #11643: A new method on Hash to grab values out of nested hashes, failing gracefully
https://bugs.ruby-lang.org/issues/11643#change-54752

* Author: Gabe Kopley
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
(I posted this to the mailing list last year [0] and received no response, but am inspired to file an issue here based on the positive reception to https://bugs.ruby-lang.org/issues/11537 )

This comes up sometimes in Rails programming [1]:

`params[:order] && params[:order][:shipping_info] && params[:order][:shipping_info][:country]`

or

`params[:order][:shipping_info][:country] rescue nil`

or

`params.fetch(:order, {}).fetch(:shipping_info, {}).fetch(:country, nil)`

What if Hash gave us a method to accomplish this more concisely and semantically?

Eg.

`params.traverse_nested_hashes_and_return_nil_if_a_key_isnt_found(:order, :shipping_info, :country)`

Or to take a nice method name suggestion [2]:

`params.dig(:order, :shipping_info, :country)`

Another example solution is https://github.com/intridea/hashie#deepfetch (Although I don't like "fetch" in this method name since it doesn't and can't take a default value as an argument like Hash#fetch does)

What do you all think?


[0] https://groups.google.com/forum/#!topic/ruby-core-google/guleNgEJWcM

[1]
https://groups.google.com/d/msg/rubyonrails-core/bOkvcvS3t_A/QXLEXwt9ivAJ
https://stackoverflow.com/questions/1820451/ruby-style-how-to-check-whether-a-nested-hash-element-exists
https://stackoverflow.com/questions/19115838/how-do-i-use-the-fetch-method-for-nested-hash
https://stackoverflow.com/questions/10130726/ruby-access-multidimensional-hash-and-avoid-access-nil-object

[2] http://stackoverflow.com/a/1820492/283398



-- 
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