iteration

Alternatives to Exceptions

Episode Summary

This week we talk about sideband data, multiple return values, and output parameters.

Episode Notes

Alternatives to Exceptions

Multiple return values in failures can be helpful -
Represent a process as an object “Download Provisionment” - This is a really interesting idea…. “MessageSend.new” - would actually handle a lot of the issues in the SMS interface concept we’ve been talking through.
“It’s tempting to raise an exception every time you get an answer you don’t like. But exception handling interrupts and obscures the flow of your business logic. Consider carefully whether a situation is truly unusual before raising an Exception.”
Diagnostics- don’t fail SO aggressively early that you don’t capture the diagnostics.

Examples of when to not "fail fast":

test suites

Sometimes you just need a way to proceed through steps and have the system tell you what parts succeeded and what parts failed

Sideband data

When communication failures without resorting to exceptions, we need a sideband: a secondary channel of communication for reporting meta-information about the status and disposition of a process.

Multiple return values

hehe, this reminds me of stuff I do in javascript

ruby supports multiple return values in the form of array splatting. in JS, you could do this with destructuring

def foo
result = 42
success = true
[result, success]
end

result, success = foo
puts "#{success ? 'succeeded' : 'failed'}; result #{result}"

Or you can use an open struct

def foo
  OpenStruct.new(:result => 42, :status => :success)
end

Output parameters

Caller-supplied fallback strategy

if we're not sure we want to terminate the execution of a long process by raising an exception, we can inject a failure policy into the process

def make_user_accounts(host, failure_policy=method(:raise))
# ...
rescue => error
failure_policy.call(error)
end

def provision_host(host, failure_policy)
make_user_accounts(host, failure_policy)
end

policy = lambda { |e| puts e.message }
provision_host("192.168.1.123", policy)

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