Using Tuples in Ruby?

Question

Does anyone use tuples in Ruby? If so, how may one implement a tuple? Ruby hashes are nice and work almost as well, but I\'d really like to see something like the Tuple clas

Answer 1

I'm the author of Gem for Ruby tuples.

You are provided with two classes:

• Tuple in general
• Pair in particular

You can initialize them in different ways:

Tuple.new(1, 2)
Tuple.new([1, 2])
Tuple(1, 2)
Tuple([1, 2])
Tuple[1, 2]

Both of the classes have some auxiliary methods:

• length / arity - which returns number of values inside tuple
• first / last / second (only pair) - which returns a corresponding elements
• [] that gives you an access to a particular elements

Answer 2

You can mock the Scala tuples with this trick :

Tuple = Struct.new(:_1, :_2)

2.2.5 :003 > t = Tuple.new("a", "b")
 => #<struct Tuple _1="a", _2="b">
2.2.5 :004 > t._1
 => "a"
2.2.5 :005 > t._2
 => "b"

but here you can't have destructuring:

2.2.5 :012 > a, b = t
 => {:_1=>"a", :_2=>"b"}
2.2.5 :013 > a
 => {:_1=>"a", :_2=>"b"}
2.2.5 :014 > b
 => nil

But thanks to this trick : https://gist.github.com/stevecj/9ace6a70370f6d1a1511 destructuring will work:

2.2.5 :001 > Tuple = Struct.new(:_1, :_2)
 => Tuple
2.2.5 :002 > t = Tuple.new("a", "b")
 => #<struct Tuple _1="a", _2="b">
2.2.5 :003 > t._1
 => "a"
2.2.5 :004 > class Tuple ; def to_ary ; to_a ; end ; end
 => :to_ary
2.2.5 :005 > a, b = t
 => #<struct Tuple _1="a", _2="b">
2.2.5 :006 > a
 => "a"
2.2.5 :007 > b
 => "b"

Answer 3

While this isn't strictly a tuple (can't do dot notation of members), you can assign a list of variables from a list, which often will solve issues with ruby being pass-by-value when you are after a list of return values.

E.g.

:linenum > (a,b,c) = [1,2,3]
:linenum > a
  => 1
:linenum > b
  => 2
:linenum > c
  => 3

Answer 4

Arrays are cool to use as tuples because of destructuring

a = [[1,2], [2,3], [3,4]]
a.map {|a,b| a+b }

Struct give you convenient . accessors

Person = Struct.new(:first_name, :last_name)
ppl = Person.new('John', 'Connor')
ppl.first_name 
ppl.last_name

You can get the convenience of both worlds with to_ary

Person = Struct.new(:first_name, :last_name) do
  def to_ary
    [first_name, last_name]
  end
end
# =>
[
  Person.new('John', 'Connor'), 
  Person.new('John', 'Conway')
].map { |a, b| a + ' ' + b  }
# => ["John Connor", "John Conway"]

Answer 5

You can do something similiar with destructuring:

def something((a, b))
  a + b
end

p something([1, 2])

This prints out 3 as expected.

Answer 6

OpenStruct?

Brief example:

require 'ostruct'

person = OpenStruct.new
person.name    = "John Smith"
person.age     = 70
person.pension = 300

puts person.name     # -> "John Smith"
puts person.age      # -> 70
puts person.address  # -> nil