Abstract¶

Make the number of arguments of Hash#merge variable.

Background¶

In many websites such as Stack Overflow and Qiita, many people are seeking how to merge more than three hashes.

https://stackoverflow.com/questions/19548496/how-to-merge-multiple-hashes-in-ruby
https://qiita.com/hc0208/items/c662f5189fa383872f4e
https://stackoverrun.com/ja/q/4997431

Many ways, like using Enumerable#inject or calling Hash#merge multiple times, are proposed, but both don't seem intuitive. Especially when using block in Hash#merge, the code becomes too complicated.

Proposal¶

Change the argument of Hash#merge from singular to variable length.

Implementation¶

https://github.com/ruby/ruby/pull/1951

Evaluation¶

The code to merge more than three hashes became much simpler and more intuitive.

before

hash1.merge(hash2).merge(hash3)
[hash1, hash2, hash3].inject do |result, part|
  result.merge(part) { |key, value1, value2| key + value1 + value2 }
end

after

hash1.merge(hash2, hash3)
hash1.merge(hash2, hash3) { |key, value1, value2| key + value1 + value2 }

Discussion¶

Summary¶

The change is needed to make Hash#merge more useful and intuitive.

If no argument is given to Hash#merge, the receiver itself is returned. In this way, Hash instance can revieve Array as arguments without concerning if the Array is empty.

hash1 = {a: 1, b: 2}
hashes = return_array_of_hashes
hash1.merge(*hashes) #=> It can't raise error even if `hashes` is empty.

• Status changed from Open to Assigned
• Assignee set to mame (Yusuke Endoh)

As I recall, Matz has accepted this ticket at the day of developers' meeting. I'll commit it soon.

• Status changed from Assigned to Closed