Issue #10984 has been updated by Cyril Vechera.


I second Ilya's opinion regarding partially ordered sets. But propose to implement the comparision similiar to classes - Hash and Class both satisfies reflexive, antisymmetric, and transitive relations. So like the Class, Hash can implement <=>, returning nil on noncomparable argument.

Take a look on classes:
<pre>
class A; end
class B; end
class BB < B; end
</pre>

How they are comparing:
<pre>
> A < B
 => nil
> B < BB
 => false
> BB < B
 => true
> A <=> B
 => nil
> B <=> BB
 => 1
</pre>



----------------------------------------
Bug #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-54993

* Author: Olivier Lacan
* Status: Closed
* Priority: Normal
* Assignee: Akira Tanaka
* ruby -v: 
* Backport: 
----------------------------------------
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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