Ruby Hash: simple immutable Hash.map() implementation for old ruby versions

hash_map.rb

class Hash
    def map_kv(&block)
        result_hash = Hash.new()
        for k,v in self
            result_item=block.call(k,v)
            result_hash[result_item.fetch("key")]=result_item.fetch("value")
        end
        return result_hash
    end
    def map_v(&block)
        result_hash = Hash.new()
        for k,v in self
            result_hash[k]=block.call(k,v)
        end
        return result_hash
    end
    def map_k(&block)
        result_hash = Hash.new()
        for k,v in self
            result_hash[block.call(k,v)]=v
        end
        return result_hash
    end
end


puts "======"
dict={"a":"A", "b":"B"}
puts dict

# map (key, value)
dict1=dict.map_kv{ |k,v| 
    
    {"key"=>k.to_s+"K1", "value"=>v+"V1"} 
}
puts dict1
# map (key)
dict2=dict.map_k{ |k,v| 

    k.to_s+"K2"
}
puts dict2
# map (value)
dict3=dict.map_v{ |k,v| 

    v+"V3"
}
puts dict3