mirror of
https://github.com/rust-lang/rustlings.git
synced 2024-12-12 11:14:55 +02:00
70 lines
2.1 KiB
Rust
70 lines
2.1 KiB
Rust
// errors2.rs
|
|
// 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 number of tokens.
|
|
// Since the player typed in the quantity, though, we get it as a string-- and
|
|
// they might have typed anything, not just numbers!
|
|
|
|
// Right now, this function isn't handling the error case at all (and isn't
|
|
// handling the success case properly either). What we want to do is:
|
|
// if we call the `parse` function on a string that is not a number, that
|
|
// function will return a `ParseIntError`, and 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! Scroll down for hints to both ways.
|
|
|
|
use std::num::ParseIntError;
|
|
|
|
pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
|
|
let processing_fee = 1;
|
|
let cost_per_item = 5;
|
|
let qty = item_quantity.parse::<i32>();
|
|
|
|
Ok(qty * cost_per_item + processing_fee)
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
|
|
#[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().to_string(),
|
|
"invalid digit found in string"
|
|
);
|
|
}
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
// One way to handle this is using a `match` statement on
|
|
// `item_quantity.parse::<i32>()` where the cases are `Ok(something)` and
|
|
// `Err(something)`. This pattern is very common in Rust, though, so there's
|
|
// a `?` operator that does pretty much what you would make that match statement
|
|
// do for you! Take a look at this section of the Error Handling chapter:
|
|
// https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
|
|
// and give it a try!
|