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Comment by Mystery-Machine | Hacker News Reader

Just out of curiosity, I never understood why people do `ENV.fetch("ANTHROPIC_API_KEY", nil)` which is the equivalent of `ENV["ANTHROPIC_API_KEY"]`. I thought the whole point of calling `.fetch` was to "fail fast". Instead of assigning `nil` as default and having `NoMethodError: undefined method 'xxx' for nil` somewhere random down the line, you could fail on the actual line where a required (not optional) ENV var wasn't found. Can someone please explain?

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There might be code later that says that if the anthropic api key is not set, then turn off the LLM feature. Wouldn't make sense for this LLM-related code but the concept makes sense for using various APIs from dev.

But if you do ENV[xxx] the value is also set to nil.

Using .fetch with a default of nil is what's arguably not very useful.

IMO it's just a robocop rule to use .fetch, which is useful in general for exploding on missing configuration but not useful if a missing value is handled.

Author here. You're actually right here.

I took the code from RubyLLM configuration documentation. If you're pulling in a lot of config options and some have default values then there's value in symmetry. Using fetch with nil communicates clearly "This config, unlike those others, has no default value". But in my case, that benefit is not there so I think I'll change it to your suggestion when I touch the code again.

This may be a Pythonism, where the exception raising convention is inverse of Ruby's.

{}["key"] # KeyError in Python

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