Introducing ?

Sometimes we just want the simplicity of unwrap without the possibility of a panic. Until now, unwrap has forced us to nest deeper and deeper when what we really wanted was to get the variable out. This is exactly the purpose of ?.

Upon finding an Err, there are two valid actions to take:

  1. panic! which we already decided to try to avoid if possible
  2. return because an Err means it cannot be handled

? is almost1 exactly equivalent to an unwrap which returns instead of panicking on Errs. Let's see how we can simplify the earlier example that used combinators:

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The try! macro

Before there was ?, the same functionality was achieved with the try! macro. The ? operator is now recommended, but you may still find try! when looking at older code. The same multiply function from the previous example would look like this using try!:

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See re-enter ? for more details.