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Simplify story and increase difficulty

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Conversion between Celsius and Fahrenheit should be understandable to
most. Inverting the formula is still not very hard, but a little harder
than only multiplying by 100.
This commit is contained in:
Remo Senekowitsch 2026-05-15 01:42:30 +02:00
parent db5ad7f42f
commit 360344ab6c
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3 changed files with 64 additions and 60 deletions
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58
exercises/23_conversions/conversions2.rs
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@ -3,50 +3,52 @@
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html
//
// Frank the fairy would like to buy some truffles from Grace the gnome, a
// world-renowned chocolatier. The truffles are priced in GnomeCoin though, and
// Frank only has FairyCredit. Help Frank by providing a `From` implementation
// to convert his FairyCredit to GnomeCoin. At the current exchange rate, one
// FairyCredit is valued at 100 GnomeCoin.
// Representing units of measurements with separate types is a common practice.
// It avoids accidentally mixing up values of different units of measurement.
#[derive(Debug)]
struct FairyCredit(u32);
struct Celsius(f64);
#[derive(Debug, PartialEq)]
struct GnomeCoin(u64);
struct Fahrenheit(f64);
impl From<FairyCredit> for GnomeCoin {
// TODO: implement From<FairyCredit> for GnomeCoin
impl From<Celsius> for Fahrenheit {
// TODO: Convert Celsius to Fahrenheit. Don't worry about floating-point
// precision. The formula is: F = C * 1.8 + 32
}
// Note that we shouldn't provide the opposite conversion: from GnomeCoin to
// FairyCredits. That's because less than 100 GnomeCoins cannot be represented
// as FairyCredits, which would make the conversion lossy. The `From` trait is
// only appropriate for infallible and lossless conversions.
impl From<Fahrenheit> for Celsius {
// TODO: Convert Fahrenheit to Celsius.
}
fn main() {
// Use the `from` function.
let g1 = GnomeCoin::from(FairyCredit(12));
println!("{g1:?}");
// Since `From` is implemented for GnomeCoin, we are able to use `Into`.
let g2: GnomeCoin = FairyCredit(9).into();
println!("{g2:?}");
// You can optionally experiment here.
}
#[cfg(test)]
mod tests {
use super::*;
const CASES: [(f64, f64); 6] = [
(-50.0, -58.0),
(0.0, 32.0),
(20.0, 68.0),
(100.0, 212.0),
(400.0, 752.0),
(1000.0, 1832.0),
];
#[test]
fn test_from() {
let g = GnomeCoin::from(FairyCredit(12));
assert_eq!(g, GnomeCoin(1200));
fn celsius_to_fahrenheit() {
for (celsius, fahrenheit) in CASES {
let Fahrenheit(actual) = Celsius(celsius).into();
assert_eq!(actual.round(), fahrenheit);
}
}
#[test]
fn test_into() {
let g: GnomeCoin = FairyCredit(9).into();
assert_eq!(g, GnomeCoin(900));
fn fahrenheit_to_celsius() {
for (celsius, fahrenheit) in CASES {
let Celsius(actual) = Fahrenheit(fahrenheit).into();
assert_eq!(actual.round(), celsius);
}
}
}

5
rustlings-macros/info.toml
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@ -1171,9 +1171,8 @@ Use the `as` operator to cast one of the operands in the last line of the
name = "conversions2"
dir = "23_conversions"
hint = """
Implement From<FairyCredit> for GnomeCoin. Check the documentation of `From` to
learn about its required items:
https://doc.rust-lang.org/std/convert/trait.From.html"""
For the conversion from Fahrenheit to Celsius, you have to determine the formula
yourself. Don't forget the order of operations!"""
[[exercises]]
name = "conversions3"

61
solutions/23_conversions/conversions2.rs
View File

@ -3,52 +3,55 @@
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html
//
// Frank the fairy would like to buy some truffles from Grace the gnome, a
// world-renowned chocolatier. The truffles are priced in GnomeCoin though, and
// Frank only has FairyCredit. Help Frank by providing a `From` implementation
// to convert his FairyCredit to GnomeCoin. At the current exchange rate, one
// FairyCredit is valued at 100 GnomeCoin.
// Representing units of measurements with separate types is a common practice.
// It avoids accidentally mixing up values of different units of measurement.
#[derive(Debug)]
struct FairyCredit(u32);
struct Celsius(f64);
#[derive(Debug, PartialEq)]
struct GnomeCoin(u64);
struct Fahrenheit(f64);
impl From<FairyCredit> for GnomeCoin {
fn from(value: FairyCredit) -> Self {
Self(value.0 as u64 * 100)
impl From<Celsius> for Fahrenheit {
fn from(Celsius(celsius): Celsius) -> Self {
Fahrenheit(celsius * 1.8 + 32.0)
}
}
// Note that we shouldn't provide the opposite conversion: from GnomeCoin to
// FairyCredits. That's because less than 100 GnomeCoins cannot be represented
// as FairyCredits, which would make the conversion lossy. The `From` trait is
// only appropriate for infallible and lossless conversions.
impl From<Fahrenheit> for Celsius {
fn from(Fahrenheit(fahrenheit): Fahrenheit) -> Self {
Celsius((fahrenheit - 32.0) / 1.8)
}
}
fn main() {
// Use the `from` function.
let g1 = GnomeCoin::from(FairyCredit(12));
println!("{g1:?}");
// Since `From` is implemented for GnomeCoin, we are able to use `Into`.
let g2: GnomeCoin = FairyCredit(9).into();
println!("{g2:?}");
// You can optionally experiment here.
}
#[cfg(test)]
mod tests {
use super::*;
const CASES: [(f64, f64); 6] = [
(-50.0, -58.0),
(0.0, 32.0),
(20.0, 68.0),
(100.0, 212.0),
(400.0, 752.0),
(1000.0, 1832.0),
];
#[test]
fn test_from() {
let g = GnomeCoin::from(FairyCredit(12));
assert_eq!(g, GnomeCoin(1200));
fn celsius_to_fahrenheit() {
for (celsius, fahrenheit) in CASES {
let Fahrenheit(actual) = Celsius(celsius).into();
assert_eq!(actual.round(), fahrenheit);
}
}
#[test]
fn test_into() {
let g: GnomeCoin = FairyCredit(9).into();
assert_eq!(g, GnomeCoin(900));
fn fahrenheit_to_celsius() {
for (celsius, fahrenheit) in CASES {
let Celsius(actual) = Fahrenheit(fahrenheit).into();
assert_eq!(actual.round(), celsius);
}
}
}