When should I use Struct vs. OpenStruct?

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In general, what are the advantages and disadvantages of using an OpenStruct as compared to a Struct? What type of general use-cases would fit each of these?

struct ruby
9 Answers

With an OpenStruct, you can arbitrarily create attributes. A Struct, on the other hand, must have its attributes defined when you create it. The choice of one over the other should be based primarily on whether you need to be able to add attributes later.

The way to think about them is as the middle ground of the spectrum between Hashes on one side and classes on the other. They imply a more concrete relationship amongst the data than does a Hash, but they don't have the instance methods as would a class. A bunch of options for a function, for example, make sense in a hash; they're only loosely related. A name, email, and phone number needed by a function could be packaged together in a Struct or OpenStruct. If that name, email, and phone number needed methods to provide the name in both "First Last" and "Last, First" formats, then you should create a class to handle it.

Pesto_239210

Other benchmark: 

require 'benchmark'
require 'ostruct'

REP = 100000

User = Struct.new(:name, :age)

USER = "User".freeze
AGE = 21
HASH = {:name => USER, :age => AGE}.freeze

Benchmark.bm 20 do |x|
  x.report 'OpenStruct slow' do
    REP.times do |index|
       OpenStruct.new(:name => "User", :age => 21)
    end
  end

  x.report 'OpenStruct fast' do
    REP.times do |index|
       OpenStruct.new(HASH)
    end
  end

  x.report 'Struct slow' do
    REP.times do |index|
       User.new("User", 21)
    end
  end

  x.report 'Struct fast' do
    REP.times do |index|
       User.new(USER, AGE)
    end
  end
end

For the impatient who wants to get an idea of the benchmark results, without running them themselves, here is the output of the code above (on an MB Pro 2.4GHz i7)

                          user     system      total        real
OpenStruct slow       4.430000   0.250000   4.680000 (  4.683851)
OpenStruct fast       4.380000   0.270000   4.650000 (  4.649809)
Struct slow           0.090000   0.000000   0.090000 (  0.094136)
Struct fast           0.080000   0.000000   0.080000 (  0.078940)
user_1315830
user_840180

Not actually an answer to the question, but a very important consideration if you care about performance. Please notice that every time you create an OpenStruct the operation clears the method cache, which means your application will perform slower. The slowness or not of OpenStruct is not just about how it works by itself, but the implications that using them bring to the whole application: https://github.com/charliesome/charlie.bz/blob/master/posts/things-that-clear-rubys-method-cache.md#openstructs

user_40856360
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