[ruby-core:71427] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash

Issue #10984 has been updated by Akira Tanaka.


Nobuyoshi Nakada wrote:
> If we'll introduce `Hash#<=` and `Hash#>=`, then `Hash#<` and `Hash#>` too?

Maybe.

Usefulness of `Hash#<` and `Hash#>` is not discussed well, though.

> `Hash` will include `Comparable` with `Hash#<=>`?

No.  It is clearly stated by matz.

```
% 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
```


----------------------------------------
Feature #10984: Hash#contain? to check whether hash contains other hash
https://bugs.ruby-lang.org/issues/10984#change-54795

* 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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