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Seatbelts
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Seatbelts save lives
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Benefits
50%
Reduction in serious injury
45%
Reduction in risk of death
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https://www.cdc.gov/motorvehiclesafety/seatbeltbrief/index.html
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Yet...
4%
of Canadian drivers
13%
of US drivers
54%
of Turkish drivers
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drive without
a seatbelt
https://en.wikipedia.org/wiki/Seat_belt_use_rates_by_country
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Why?
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Find them
uncomfortable
Over 65s find them
restricting
Do not think they
ever need them
Think they’re less likely
to have an accident
https://www.bbc.com/news/blogs-magazine-monitor-29416372
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“But cars are safe. We test them!”
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- Costs too much ⏱ and
- Cannot test every situation
(Crash)
Testing
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The higher the stakes, the safer the car
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Ufuk Kayserilioğlu
Rails and Ruby Infrastructure Team
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Shopify Scale
Commerce 1M
Merchants
8000
orders/min (peak)
12B
USD sales/year
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135B
USD total sales
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Shopify Scale
Engineering 1500
RnD Employees
~21K
Ruby files
~150K
tests
12
~40
deploys daily
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There is too much at stake here.
We need seatbelts!
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Adopting Sorbet at Scale
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Sorbet
01
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Sorbet
﹘ fast
﹘ expressive
﹘ static
﹘ gradual
type checker for Ruby
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def foo(opts)
opts.fetch("bar")
end
foo(bar: 1)
foo.rb
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# typed: true
extend(T::Sig)
sig do
params(opts: T::Hash[Symbol, Integer])
.returns(Integer)
end
def foo(opts)
opts.fetch("bar")
end
foo(bar: 1)
foo.rb
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foo.rb:9: Expected Symbol but found String("bar") for argument arg0
https://srb.help/7002
10 | opts.fetch("bar")
^^^^^^^^^^^^^^^^^
hash.rbi#L517: Method Hash#fetch has specified arg0 as Symbol
517 | arg0: K,
^^^^
Got String("bar") originating from:
foo.rb:9:
10 | opts.fetch("bar")
^^^^^
Errors: 1
srb tc
foo.rb
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# typed: true
require "view_gem"
View.render
foo.rb
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view.rbi
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# typed: true
require "view_gem"
View.render
foo.rb
# typed: true
class View
def self.render(file)
end
end
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view.rbi
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# typed: true
require "view_gem"
View.render
# ^ error: Not enough
arguments provided for
method View.render.
Expected: 1, got: 0
foo.rb
# typed: true
class View
def self.render(file)
end
end
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Our Journey
02
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Sorbet is mandatory
in CI
May
2019
Sorbet over
all files
Mar
2019
Sorbet is
open-sourced
Jun
2019
Shopify gets access
to Sorbet
Jul
2018
Sorbet introduced
in Core
Oct
2018
Timeline
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We paid the
early adopter price
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Built a runtime component
No runtime component
Problem
﹘ Initial version built in-house (waffle-cone)
﹘ Shared our work with the Sorbet team
﹘ Later on switched to sorbet-runtime
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Built a gem RBI generator
All constants must resolve
Problem
﹘ Initial version built on YARD
﹘ Decided that structure of constants more important
﹘ Built a runtime reflection based tool
﹘ Open sourced as tapioca
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Built Rubocop rules
Some Ruby constructs are not supported
Problem
﹘ Initial rules bundled with waffle-cone
﹘ Extracted out to rubocop-sorbet
﹘ Open sourced
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Built DSL plugins for Sorbet
Metaprogramming
Problem
﹘ Based on simple class method name matching
﹘ Can run Ruby scripts to generate interface
﹘ Contributed to Sorbet, documented
﹘ Slow and error-prone
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RBI generator for models
Rails support
Problem
﹘ Rake task to generate RBI files for AR models
﹘ Based on sorbet-rails
﹘ Planning switch to sorbet-rails
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Results
03
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Strictness
levels of
non-test files
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Percentage
of checked
calls
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Developer
invocations
of type check
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Evolution of
method
signatures
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Testimonials
Likes
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“We get quicker feedback than
tests or CI”
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Testimonials
Likes
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“Allowed us to write less tests”
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Testimonials
Likes
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“Both static and runtime type
checkers caught errors not
caught by tests alone”
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Testimonials
Likes
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“Improves code quality,
encourages better code design”
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Testimonials
Likes
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“Evergreen documentation,
makes onboarding easier”
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Testimonials
Dislikes
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“Syntax is verbose, it is not DRY”
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Testimonials
Dislikes
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“Hard to add types to existing
code”
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Testimonials
Dislikes
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“Rails and metaprogramming
support is not complete yet”
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Pitfalls
04
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Metaprogramming support
﹘ If you use a lot of DSLs, you will need to
generate RBI files for them.
﹘ Limited ability to extend Sorbet to understand
more syntax. DSL plugins too slow.
Pitfall 1
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Some missing stdlib signatures
﹘ Stdlib/core method signatures are maintained
by the Sorbet team.
﹘ No full coverage, so you might get some errors
for perfectly valid Ruby code.
﹘ Contribute missing signatures back to Sorbet.
Pitfall 2
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No constants via inheritance
class Foo
Bar = 42
end
class Baz < Foo
end
Baz::Bar # error: Unable to resolve constant Bar
Foo::Bar # ok
Pitfall 3
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No dynamic superclass/mixin
def superclass
Class.new
end
def mixin
Module.new
end
class Baz < superclass
# error: ^ Superclasses must only contain constant literals
include mixin
# error: ^ include must only contain constant literals
end
Pitfall 4
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Runtime type checking overhead
﹘ Checking types at runtime adds ~7% overhead.
﹘ Not a problem for dev and test.
﹘ Might not want it for production.
Pitfall 5
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How to get started
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Sorbet Playground
﹘ Play around at https://sorbet.run to get familiar
﹘ Read the docs at https://sorbet.org/docs/
Step 1
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Add Sorbet to your project
﹘ Add sorbet, sorbet-runtime to your
Gemfile
﹘ Run bundle exec srb init
Step 2
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Add Sorbet to your project
﹘ Add sorbet, sorbet-runtime and tapioca
to your Gemfile
﹘ Run bundle exec tapioca init
﹘ Run bundle exec tapioca sync
Step 2 (alt)
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Start by typing new code
﹘ Easier to type when adding new code.
﹘ Add types to existing code when it is easy and
convenient.
﹘ Use rubocop-sorbet to add template
signatures to existing code in bulk
Step 3
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Lean on gradual typing
﹘ You can type as much or as little as you want.
﹘ Start small, increase coverage slowly.
﹘ Don’t break other people’s workflows.
Step 4
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Don’t overtype
﹘ It is OK to use simpler signatures
﹘ There is no harm in using T.untyped when
needed.
﹘ Your colleagues should not need a PhD in type
theory to make code changes.
Step 5
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Track your progress
﹘ Sorbet metrics via --metrics-file flag
﹘ Easy to parse JSON format
﹘ Set up a nightly task and dashboard to track
progress
Step 6
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Thank you
Don’t forget to fasten your seatbelts!
Reach out to me
Twitter: @paracycle
Github: @paracycle
Join us at the Shopify booth!