From: akr@...
Date: 2015-11-11T05:33:29+00:00
Subject: [ruby-core:71440] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash

Issue #10984 has been updated by Akira Tanaka.


Akira Tanaka wrote:

> ```
> % ruby -e '
> class Hash
>   def <=(other)
>     self.merge(other) == other
>   end
>   def >=(other)
>     self.merge(other) == self
>   end
>   def <(other)
>     self <= other && self != other
>   end
>   def >(other)
>     self >= other && self != other
>   end
> end
> hs = [{a:1, b:2}, {a:1, b:2, c:3}]
> ops = %w[<= >= < >]
> ops.each {|op|
>   hs.each {|h1|
>     hs.each {|h2|
>       puts "#{h1} #{op} #{h2} = #{h1.send(op, h2)}"
>     }
>   }
> }
> '
> {:a=>1, :b=>2} <= {:a=>1, :b=>2} = true
> {:a=>1, :b=>2} <= {:a=>1, :b=>2, :c=>3} = true
> {:a=>1, :b=>2, :c=>3} <= {:a=>1, :b=>2} = false
> {:a=>1, :b=>2, :c=>3} <= {:a=>1, :b=>2, :c=>3} = true
> {:a=>1, :b=>2} >= {:a=>1, :b=>2} = true
> {:a=>1, :b=>2} >= {:a=>1, :b=>2, :c=>3} = false
> {:a=>1, :b=>2, :c=>3} >= {:a=>1, :b=>2} = true
> {:a=>1, :b=>2, :c=>3} >= {:a=>1, :b=>2, :c=>3} = true
> {:a=>1, :b=>2} < {:a=>1, :b=>2} = false
> {:a=>1, :b=>2} < {:a=>1, :b=>2, :c=>3} = true
> {:a=>1, :b=>2, :c=>3} < {:a=>1, :b=>2} = false
> {:a=>1, :b=>2, :c=>3} < {:a=>1, :b=>2, :c=>3} = false
> {:a=>1, :b=>2} > {:a=>1, :b=>2} = false
> {:a=>1, :b=>2} > {:a=>1, :b=>2, :c=>3} = false
> {:a=>1, :b=>2, :c=>3} > {:a=>1, :b=>2} = true
> {:a=>1, :b=>2, :c=>3} > {:a=>1, :b=>2, :c=>3} = false
> ```

For the record, this sample implementation was wrong.

It should consider that two hashs may have different values for same key.

```
% ruby -e '
class Hash
  def <=(other)
    self.merge(other) {|k,v1,v2| v1 } == other
  end
  def >=(other)
    self.merge(other) {|k,v1,v2| v2 } == self
  end
  def <(other)
    self <= other && self != other
  end
  def >(other)
    self >= other && self != other
  end
end
hs = [{a:1}, {a:2}]
ops = %w[<= >= < >]
ops.each {|op|
  hs.each {|h1|
    hs.each {|h2|
      puts "#{h1} #{op} #{h2} = #{h1.send(op, h2)}"
    }
  }
}
'
{:a=>1} <= {:a=>1} = true
{:a=>1} <= {:a=>2} = false
{:a=>2} <= {:a=>1} = false
{:a=>2} <= {:a=>2} = true
{:a=>1} >= {:a=>1} = true
{:a=>1} >= {:a=>2} = false
{:a=>2} >= {:a=>1} = false
{:a=>2} >= {:a=>2} = true
{:a=>1} < {:a=>1} = false
{:a=>1} < {:a=>2} = false
{:a=>2} < {:a=>1} = false
{:a=>2} < {:a=>2} = false
{:a=>1} > {:a=>1} = false
{:a=>1} > {:a=>2} = false
{:a=>2} > {:a=>1} = false
{:a=>2} > {:a=>2} = false
```

Note that nobu's implementation already committed has no problem.


----------------------------------------
Feature #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-54808

* 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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