From: hi@...
Date: 2015-08-18T04:30:09+00:00
Subject: [ruby-core:70444] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash

Issue #10984 has been updated by Olivier Lacan.


I didn't notice the notes from [DevelopersMeeting20150514Japan](https://docs.google.com/document/u/1/d/1kEsXwy0X046Z0RqsvWv6O-gJ-tLY91Mc0vDHYZoJE1M/pub) before so I'll link to my original musings about `Hash#include?` which later evolved into this feature/patch: [**Proposal for a better Ruby Hash#include?**](http://olivierlacan.com/posts/proposal-for-a-better-ruby-hash-include/)

I'm aware this post needs revision and more concrete examples and use cases. I'll try to bring that together soon.

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Feature #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-53853

* Author: Olivier Lacan
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
Comparing hashes seems like a common practice but there currently isn't a method to ask a 
hash instance whether it includes another hash instance.

The most intuitive method to reach for would be `Hash#include?` but it is in fact an alias to `Hash#has_key?`

What I'm looking for can be achieved with:

~~~
class Hash
  def contain?(other)
    self.merge(other) == self
  end
end
~~~

Here's a simple demo of `#contain?` in use:

~~~
{ a: true, b: false }.contain?({ a: true})
# => true

{ a: true, b: false }.contain?({ b: false})
# => true

{ a: true, b: false }.contain?({ a: false})
# => false

{ a: true, b: false }.contain?({ c: true})
# => false
~~~

One important note is that this method is *not checking for nested hash matches*.
This may need to be addressed when the parameters include a nested hash perhaps.

Thanks to Terence Lee's help, nobu created a patch for this feature last year. 
I've only modified the name of the method from [his original patch](https://gist.github.com/nobu/dfe8ba14a48fc949f2ed) and attached it to this issue.

---Files--------------------------------
Hash#contain_.patch (2.22 KB)


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