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Extremely Defensive Coding
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a!/samphippen
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Who is having fun?
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Who is here for their first time?
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I want to start with a story
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“When is it OK to override the methods on object?”
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I umm’d and ahh’d for a bit
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I gave a half explanation and then asked them if they understood
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I eventually came to an answer to do with consistency
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Do it when it makes your object more consistent with Ruby, not less
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e.g. an == on a data object
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What makes a gem good?
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Internals?
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Internals?
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Interface?
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Interface? ✅
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More convenient than if I did it myself
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And it stays convenient
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And it can be used by everyone on a team
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And it works with a wide range of Ruby codebases
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RSpec
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RSpec Definitely always convenient
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RSpec Definitely always convenient
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User story
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As an RSpec user
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When I stub an object
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I want the original method to be on that object after the example
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So that my objects aren’t broken by my test suite
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As an RSpec user
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When I stub an object
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I want the original method to be on that object after the example
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So that my objects aren’t broken by my test suite
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How does that work?
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allow(cat).to receive(:meow)
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Takes the meow method off cat
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Saves it
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Executes test
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Puts the method back on the original object
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How do you save a method?
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No content
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Method object
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Put it somewhere else
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Put it back at end of test
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The end
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The end
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Defensive coding
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RSpec::Support .method_handle_for
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Simply invoking the method method is not good enough
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Some scenes may have been altered/accelerated for your viewing pleasure
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Let’s have some questions !/samphippen
[email protected]
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Users Lie
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def method ‘get’ end
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Users can redefine anything at any time in Ruby
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and that’s fine
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Instance method object Method without a target object
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Comes from a class/module not an instance
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Grab the Kernel implementation of #method
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Users can and will redefine core methods at any time
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Instead we use Kernel’s implementation
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Nobody screws with Kernel
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Ruby interpreters lie
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Some objects do not have Kernel in their inheritance chain
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Rebinding module methods
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c
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c
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RSpec does not support Rubinius
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We tried, we really really tried
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So anyway, dealing with module methods
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Ruby interpreters behave differently.
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Let’s have some questions !/samphippen
[email protected]
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Sometimes users don’t lie
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`method': undefined method `foo' for class `Foo' (NameError)
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This is a catch 22
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Solution: trust but verify
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Let’s put it all together
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Wrapping up
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This is why I love RSpec
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Please file bugs
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Your gem should be defensive
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Users lie Redefinitions come from anywhere, expect them
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Ruby interpreters lie Your code will run on non-MRI, old MRI, etc
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Sometimes users don’t lie Users are weird, trust but verify
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What makes a gem good?
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Internals?
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That explanation made no sense
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Internals?
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Interface?
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allow(cat).to receive(:meow)
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You get the complexity of RSpec working with any object for free
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You probably didn’t even know it was there until I just told you
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Interface? ✅
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Gems
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Gems provide strong abstraction boundaries
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Done badly they cause an even more extreme mess
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Done correctly they hide huge complexity behind well defined barriers
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Defending against users helps your gem be convenient
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Write defensively, and your users will never know what’s inside the box
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Remember the story?
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This talk is born out of Ruby’s power
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We need our code to defend today, against the mistakes of our tomorrow
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Let’s have some questions !/samphippen
[email protected]
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Let’s have some questions !/samphippen
[email protected]
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Minitest Mock is 169 lines of code
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I just showed you more code than that
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For a tiny feature that isn’t a complete mocking library
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and that’s fine
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Please check out https://browserpath.co
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Let’s have some questions a!/samphippen
[email protected]