mirror of
https://github.com/notohh/rustlings.git
synced 2024-11-29 00:34:17 -05:00
58 lines
1.8 KiB
Rust
58 lines
1.8 KiB
Rust
// Say we're writing a game where you can buy items with tokens. All items cost
|
|
// 5 tokens, and whenever you purchase items there is a processing fee of 1
|
|
// token. A player of the game will type in how many items they want to buy, and
|
|
// the `total_cost` function will calculate the total cost of the items. Since
|
|
// the player typed in the quantity, we get it as a string. They might have
|
|
// typed anything, not just numbers!
|
|
//
|
|
// Right now, this function isn't handling the error case at all. What we want
|
|
// to do is: If we call the `total_cost` function on a string that is not a
|
|
// number, that function will return a `ParseIntError`. In that case, we want to
|
|
// immediately return that error from our function and not try to multiply and
|
|
// add.
|
|
//
|
|
// There are at least two ways to implement this that are both correct. But one
|
|
// is a lot shorter!
|
|
|
|
use std::num::ParseIntError;
|
|
|
|
#[allow(unused_variables)]
|
|
fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
|
|
let processing_fee = 1;
|
|
let cost_per_item = 5;
|
|
|
|
// Added `?` to propagate the error.
|
|
let qty = item_quantity.parse::<i32>()?;
|
|
// ^ added
|
|
|
|
// Equivalent to this verbose version:
|
|
let qty = match item_quantity.parse::<i32>() {
|
|
Ok(v) => v,
|
|
Err(e) => return Err(e),
|
|
};
|
|
|
|
Ok(qty * cost_per_item + processing_fee)
|
|
}
|
|
|
|
fn main() {
|
|
// You can optionally experiment here.
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
use std::num::IntErrorKind;
|
|
|
|
#[test]
|
|
fn item_quantity_is_a_valid_number() {
|
|
assert_eq!(total_cost("34"), Ok(171));
|
|
}
|
|
|
|
#[test]
|
|
fn item_quantity_is_an_invalid_number() {
|
|
assert_eq!(
|
|
total_cost("beep boop").unwrap_err().kind(),
|
|
&IntErrorKind::InvalidDigit,
|
|
);
|
|
}
|
|
}
|