From: hi@... Date: 2015-11-03T23:38:02+00:00 Subject: [ruby-core:71321] [Ruby trunk - Feature #10984] Hash#contain? to check whether hash contains other hash Issue #10984 has been updated by Olivier Lacan. Assignee set to Akira Tanaka Responding to feedback from Akira Tanaka and Nobuyoshi Nakada at [DevelopersMeeting20150514Japan](https://docs.google.com/document/u/1/d/1kEsXwy0X046Z0RqsvWv6O-gJ-tLY91Mc0vDHYZoJE1M/pub) > akr: ���contain��� is too general. ���subhash���? You mean something like this? ``` { a: 1, b: 2 }.subhash?({ b: 2 }) ``` Semantically, this feels strange to me. It doesn't seem obvious at all which hash we're checking for a subhash on and I would expect a lot of confusion with a method name like this. Compare to: ``` { a: 1, b: 2 }.contains?({ b: 2 }) ``` I believe contains is semantically far more self-evident. It also seems odd to introduce a `sub?` method name for this since I'm not aware of any similar method names for classes that would have similar behavior. --- > n0kada: ���contain?��� seems similiar to ���include?��� It is. Sadly, I've been told repeatedly that it's a bad idea to try to change the behavior of `include?`. I would prefer replacing the existing `include?` but I will settle for `contains?` for now because the meaning of "contain" focuses on what's inside the object under observation and is far more commonly used than "comprise": ~~~ contain |k��n��t��n| verb [ with obj. ] 1. have or hold (someone or something) within: coffee cans that once contained a full pound of coffee. - be made up of (a number of things); consist of: borscht can contain mainly beets or a number of vegetables. - (of a number) be divisible by (a factor) without a remainder. ~~~ --- > akr: do we really use? we need concrete examples. Yes, RSpec has an ad-hoc implementation of this feature in its `include` matcher: https://github.com/rspec/rspec-expectations/blob/bb731e29f7800f5cef736cf8850293276a0d3f90/lib/rspec/matchers/built_in/include.rb#L94-L97 RSpec has been downloaded 29 Million times on RubyGems. I think this is a legitimate use case. This would simplify not only RSpec's internal code for Hash matchers, but any existing application who depends on this code, for a relatively minimal impact on the core Hash codebase (see provided patch). I expanded on my original proposal (since then changed from Hash#include? to Hash#contains?) here: http://olivierlacan.com/posts/proposal-for-a-better-ruby-hash-include/ ---------------------------------------- Feature #10984: Hash#contain? to check whether hash contains other hash https://bugs.ruby-lang.org/issues/10984#change-54696 * 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) -- https://bugs.ruby-lang.org/