RecapDifficulty: Advanced1 min

Recap: Optional

What the type says, how to unwrap it, the two traps, and where it belongs, with where each was.

Optional comes down to the five ideas below, each listed with the card that covers it.

What the topic established, and which card it was on
The idea	Where
`Optional` puts "there might be nothing" into the signature	Optional: A Return Type That Says There Might Be Nothing
`orElse` for a value in hand, `orElseGet` for anything that costs	orElse vs orElseGet vs orElseThrow
The argument to `orElse` is computed whether or not it is needed	orElse Runs Its Fallback Even When the Value Is Present
`get()` without a check throws, exactly as the null would have	Optional.get() Without a Check Brings the Null Bug Back
A return type, never a field, a parameter or an element	Where Optional Does Not Belong: Fields, Parameters and Collections

Optional makes absence visible and does not make anybody handle it. Everything that goes wrong with it is a caller unwrapping it immediately, which puts the original problem back under a longer name.

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