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Talk a bit about the contract of Guess

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Carol (Nichols || Goulding) 2016-10-17 16:41:14 -04:00
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src/ch09-03-to-panic-or-not-to-panic.md
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@ -135,6 +135,12 @@ impl Guess {
Listing 9-8: A `Guess` type that will only hold values between 1 and 100
</caption>
If code calling `Guess::new` passed in a value that was not between 1 and 100,
that would be a violation of the contract that `Guess::new` is relying on. This
function needs to signal to the calling code that it has a bug somewhere
leading to the contract violation. The conditions in which `Guess::new` might
panic should be discussed in its public-facing API documentation.
Important to note is the `value` field of the `Guess` struct is private, so
code using this struct may not set that value directly. Callers *must* use the
`Guess::new` constructor function to create an instance of `Guess`, and they