mirror of https://github.com/rust-lang/rustlings
You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
68 lines
1.6 KiB
Rust
68 lines
1.6 KiB
Rust
// errors3.rs
|
|
// This is a program that is trying to use a completed version of the
|
|
// `total_cost` function from the previous exercise. It's not working though--
|
|
// we can't call the `try!` macro in the `main()` function! Why not?
|
|
// What should we do instead? Scroll for hints!
|
|
|
|
use std::num::ParseIntError;
|
|
|
|
fn main() {
|
|
let mut tokens = 100;
|
|
let pretend_user_input = "8";
|
|
|
|
let cost = try!(total_cost(pretend_user_input));
|
|
|
|
if cost > tokens {
|
|
println!("You can't afford that many!");
|
|
} else {
|
|
tokens -= cost;
|
|
println!("You now have {} tokens.", tokens);
|
|
}
|
|
}
|
|
|
|
pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
|
|
let processing_fee = 1;
|
|
let cost_per_item = 5;
|
|
let qty = try!(item_quantity.parse::<i32>());
|
|
|
|
Ok(qty * cost_per_item + processing_fee)
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
// Since the `try!` macro returns an `Err` early if the thing it's trying to
|
|
// do fails, you can only use the `try!` macro in functions that have a
|
|
// `Result` as their return type.
|
|
|
|
// The error that you get if you run this code is:
|
|
|
|
// ```
|
|
// error: mismatched types:
|
|
// expected `()`,
|
|
// found `std::result::Result<_, _>`
|
|
// ```
|
|
|
|
// which is saying that the expected return type of the `main` function is
|
|
// the empty tuple, but we tried to return a `Result`-- and that's happening
|
|
// in the implementation of `try!`. The `main` function never has a return type,
|
|
// so we have to use another way of handling a `Result` within `main`.
|
|
|
|
// Decide what we should do if `pretend_user_input` has a string value that does
|
|
// not parse to an integer, and implement that instead of calling the `try!`
|
|
// macro.
|