Original Issue: https://bugs.ruby-lang.org/issues/11286
Read the docs too, they’re awesome and they help with anything I mention in here you don’t recognize: Module: Enumerable (Ruby 2.4.2) Module : Enumerable - Ruby 2.4.2ruby-doc.org
Triple Equals Black Magic
If you haven’t yet, I would highly suggest you read into my previous post over Triple Equals: Triple Equals Black Magic For the most part, === is either ignored or used in the background of case statements. Now there are several articles…medium.com
It will fill your mind with all types of bad ideas in the next few paragraphs for what we might be able to do with this new feature.
The Predicate Methods
First off, what do I mean when I say predicates? I’m referring to the predicate-style methods in Enumerable, the ones that end with a question mark:
[1,2,3].all? { |n| n.even? } # => false
[2,4,6].all? { |n| n.even? } # => true
[1,2,3].any? { |n| n.even? } # => true
[1,3,5].any? { |n| n.even? } # => false
[1,2,3].none? { |n| n.even? } # => false
[1,3,5].none? { |n| n.even? } # => true
We’ll get back to the short-hand variants later, but for now this will do as a base example.
Grepping for an Answer
Now there’s another method in Enumerable that’s easy for us to forget about called grep:
[1,2,3, 'string'].grep(Numeric) # => [1, 2, 3]
Now what does the doc say about how it works?
Returns an array of every element in enum for which Pattern === element.
Y’know, that’s already kinda useful knowing what we can do with triple equals, but one brave Rubyist decided to give that a little extra nudge.
Triple Equals with Predicate Methods
Now we get to the point.
What would happen if our predicate friends up there decided it was right time to take a single arity argument that responds nicely to === like grep?
Magic. Magic would happen.
%w(foo bar baz).none?(/foo/) # => false
[1,2,3].all?(Numeric) # => true
Interesting, but not quite magic. A bit further?
%w(10.0.0.1 10.0.0.5).all?(IPAddr.new('10.0.0.0/8'))
Nifty if we’re SysAdmins, but a bit more perhaps.
Black Magic is Fun
Remember how we can define our own ===? It’s time to jump that rabbit hole.
What if we made a wrapper method that’d let us do things with Arrays and Hashes to have some more fun? Oh lots of fun, lots indeed!
Just note: THIS IS NOT GOOD RUBY
Let’s borrow our people data from the Triple Equals Black Magic post:
people = [
{name: 'Bob', age: 20},
{name: 'Sue', age: 30},
{name: 'Jack', age: 10},
{name: 'Jill', age: 4},
{name: 'Jane', age: 5}
]
To start out with we’re going to need to get our wrapper made:
class Q
def initialize(conds = {}) @conds = conds end
def ===(other)
@conds.all? { |k, matcher| matcher === other[k] }
end
end
def Q(conds = {}) Q.new(conds) end
Now let’s try this one out:
people.any?(Q(age: 1..10)) # => true
Nifty! Though you could technically use this trick already with to_proc :
class Q
def initialize(conds = {}) @conds = conds end
def ===(other)
@conds.all? { |k, matcher| matcher === other[k] }
end
def to_proc
-> other { self === other }
end
end
def Q(conds = {}) Q.new(conds) end
people.select(&Q(age: 20))
Still fun. Well, I had fun at least.
When Do We Get the Toys?
Well, that’s the gotcha. We’re not exactly sure yet, but it’s been blessed by good sir Matz:
OK, I made a decision. I took option 1 above as proposed. We can do as following: [1, 3.14, 2ri].all?(Numeric) # => true if should_be_all_symbols.any?(String) … end some_strings.none?(/aeiou/i) Matz.
With some luck we may even see it in 2.5 this Christmas, but who knows. I’m still excited for it either way.
Liked the Lemurs?
Notice the Lemurs floating around? They’re from the book I’m working on: Title · An Illustrated Guide to Ruby Learn Ruby with Lemurs and Puns!baweaver.gitbooks.io
Finishing Up
I like new features, we all do, but remember to be patient as they make their way through the bug trackers. The core team does an amazing job, people like me just get excited a bit early and peek at our presents before Christmas.