From: hi@...
Date: 2015-11-17T23:54:29+00:00
Subject: [ruby-core:71534] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash

Issue #10984 has been updated by Olivier Lacan.


Ilya Vorontsov wrote:
> So why one can sort this array and which result does one expect?:
> 
> ```ruby
> [{}, {a:1,b:2}, {c:3}, {a:1}, {b:2}].sort
> ```

This is the actual result with 2.3.0-preview1:

```ruby
RUBY_VERSION
=> "2.3.0"
 [{}, {a:1,b:2}, {c:3}, {a:1}, {b:2}].sort
ArgumentError: comparison of Hash with Hash failed
```

Maybe I'm reading you too quickly or I'm too tired but did you note that `<=>` is **not** implemented on Hash? Matz made that clear and Akira Tanaka clarified it in [this response](https://bugs.ruby-lang.org/issues/10984#note-11).

----------------------------------------
Feature #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-54913

* Author: Olivier Lacan
* Status: Closed
* 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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