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Merged
merged 2 commits into from
Mar 2, 2018
Merged

nth-prime: Provide a function template #437

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c70be04
nth-prime: Change return type wrapper from Result to Option
cbzehner Mar 1, 2018
2e50c9b
nth-prime: Add function template
cbzehner Mar 1, 2018
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8 changes: 4 additions & 4 deletions exercises/nth-prime/example.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,10 +9,10 @@ fn is_prime(n: u32) -> bool {
return true;
}

pub fn nth(n: u32) -> Result<u32, ()> {
pub fn nth(n: u32) -> Option<u32> {
match n {
0 => Err(()),
1 => Ok(2),
0 => None,
1 => Some(2),
_ => {
let mut count: u32 = 1;
let mut candidate: u32 = 1;
Expand All @@ -22,7 +22,7 @@ pub fn nth(n: u32) -> Result<u32, ()> {
count += 1;
}
}
Ok(candidate)
Some(candidate)
}
}
}
3 changes: 3 additions & 0 deletions exercises/nth-prime/src/lib.rs
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@@ -0,0 +1,3 @@
pub fn nth(n: u32) -> Option<u32> {
unimplemented!("What is the {}th prime number?", n)
}
10 changes: 5 additions & 5 deletions exercises/nth-prime/tests/nth-prime.rs
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Expand Up @@ -2,29 +2,29 @@ extern crate nth_prime as np;

#[test]
fn test_first_prime() {
assert_eq!(np::nth(1), Ok(2));
assert_eq!(np::nth(1), Some(2));
}

#[test]
#[ignore]
fn test_second_prime() {
assert_eq!(np::nth(2), Ok(3));
assert_eq!(np::nth(2), Some(3));
}

#[test]
#[ignore]
fn test_sixth_prime() {
assert_eq!(np::nth(6), Ok(13));
assert_eq!(np::nth(6), Some(13));
}

#[test]
#[ignore]
fn test_big_prime() {
assert_eq!(np::nth(10001), Ok(104743));
assert_eq!(np::nth(10001), Some(104743));
}

#[test]
#[ignore]
fn test_zeroth_prime() {
assert!(np::nth(0).is_err());
assert_eq!(np::nth(0), None);
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Changing this from assert! to assert_eq! was a good call, the error message goes from:

---- test_zeroth_prime stdout ----
	thread 'test_zeroth_prime' panicked at 'assertion failed: np::nth(0).is_none()', tests/nth-prime.rs:28:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

to the much clearer

---- test_zeroth_prime stdout ----
	thread 'test_zeroth_prime' panicked at 'assertion failed: `(left == right)`
  left: `Some(1)`,
 right: `None`', tests/nth-prime.rs:28:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

You can see the full output of both options here.

}