From: hi@...
Date: 2015-11-09T15:06:32+00:00
Subject: [ruby-core:71419] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash

Issue #10984 has been updated by Olivier Lacan.


Yukihiro Matsumoto wrote:
> Hash#contain? has slight ambiguity problem.  I'd vote for adding `>=`, along with '<='.
> 
> Matz.

Thanks for considering this feature, Matz. :-)

If I understand correctly, the following examples would be correct?

```
{ a: 1, b: 2 } >=  { b: 2 }
=> true
{ b: 2 } <=  { a: 1, b: 2 }
=> true

# also
{ b: 2 } >=  { b: 2 }
=> true
{ a: 1 } >=  { b: 2 }
=> false

{ b: 2 } <=  { b: 2 }
=> true
{ b: 2 } <=  { a: 1 }
=> false
```

I think the versatility of this alone would make it even more useful than the one direction method I suggested. 

----------------------------------------
Feature #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-54788

* Author: Olivier Lacan
* Status: Open
* Priority: Normal
* Assignee: Akira Tanaka
----------------------------------------
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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