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c21fb10ae4
In the case where you'd like to provide an explanation why the function isn't able to do the thing, rather than just not doing the thing.
72 lines
1.8 KiB
Rust
72 lines
1.8 KiB
Rust
// This function refuses to generate text to be printed on a nametag if
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// you pass it an empty string. It'd be nicer if it explained what the problem
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// was, instead of just sometimes returning `None`. The 2nd test currently
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// does not compile or pass, but it illustrates the behavior we would like
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// this function to have.
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// Scroll down for hints!!!
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pub fn generate_nametag_text(name: String) -> Option<String> {
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if name.len() > 0 {
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Some(format!("Hi! My name is {}", name))
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} else {
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// Empty names aren't allowed.
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None
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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// This test passes initially if you comment out the 2nd test.
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// You'll need to update what this test expects when you change
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// the function under test!
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#[test]
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fn generates_nametag_text_for_a_nonempty_name() {
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assert_eq!(
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generate_nametag_text("Beyoncé".into()),
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Some("Hi! My name is Beyoncé".into())
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);
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}
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#[test]
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fn explains_why_generating_nametag_text_fails() {
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assert_eq!(
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generate_nametag_text("".into()),
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Err("`name` was empty; it must be nonempty.".into())
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);
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}
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}
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// `Err` is one of the variants of `Result`, so what the 2nd test is saying
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// is that `generate_nametag_text` should return a `Result` instead of an
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// `Option`.
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// To make this change, you'll need to:
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// - update the return type in the function signature to be a Result that
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// could be the variants `Ok(String)` and `Err(String)`
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// - change the body of the function to return `Ok(stuff)` where it currently
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// returns `Some(stuff)`
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// - change the body of the function to return `Err(error message)` where it
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// currently returns `None`
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// - change the first test to expect `Ok(stuff)` where it currently expects
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// `Some(stuff)`.
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