When should I use Struct vs. OpenStruct?

Question

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?

Answer 1

UPDATE:

As of Ruby 2.4.1 OpenStruct and Struct are much closer in speed. See https://stackoverflow.com/a/43987844/128421

PREVIOUSLY:

For completeness: Struct vs. Class vs. Hash vs. OpenStruct

Running similar code as burtlo's, on Ruby 1.9.2, (1 of 4 cores x86_64, 8GB RAM) [table edited to align columns]:

creating 1 Mio Structs :         1.43 sec ,  219 MB /  90MB (virt/res)
creating 1 Mio Class instances : 1.43 sec ,  219 MB /  90MB (virt/res)
creating 1 Mio Hashes  :         4.46 sec ,  493 MB / 364MB (virt/res)
creating 1 Mio OpenStructs :   415.13 sec , 2464 MB / 2.3GB (virt/res) # ~100x slower than Hashes
creating 100K OpenStructs :     10.96 sec ,  369 MB / 242MB (virt/res)

OpenStructs are sloooooow and memory intensive , and don't scale well for large data sets

Creating 1 Mio OpenStructs is ~100x slower than creating 1 Mio Hashes.

start = Time.now

collection = (1..10**6).collect do |i|
  {:name => "User" , :age => 21}
end; 1

stop = Time.now

puts "#{stop - start} seconds elapsed"

Answer 2

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)

Answer 3

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