2.5.1 解答

Tue, 11 Aug 2026 11:30:00 +0800
译文 · 基于 Comprehensive Rust
原文链接: https://google.github.io/comprehensive-rust/borrowing/solution.html
2.5.1 解答

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// Copyright 2023 Google LLC
// SPDX-License-Identifier: Apache-2.0
struct Spell {
 name: String,
 cost: u32,
 uses: u32,
}

struct Wizard {
 spells: Vec<Spell>,
 mana: u32,
}

impl Wizard {
 fn new(mana: u32) -> Self {
 Wizard { spells: vec![], mana }
 }

 fn add_spell(&mut self, spell: Spell) {
 self.spells.push(spell);
 }

 fn cast_spell(&mut self, name: &str) {
 let mut spell_idx = None;
 for idx in 0..self.spells.len() {
 if self.spells[idx].name == name {
 spell_idx = Some(idx);
 break;
 }
 }

 let Some(idx) = spell_idx else {
 println!("Spell {} not found!", name);
 return;
 };

 let spell = &mut self.spells[idx];
 if self.mana >= spell.cost {
 self.mana -= spell.cost;
 spell.uses -= 1;
 println!(
 "Casting {}! Mana left: {}. Uses left: {}",
 spell.name, self.mana, spell.uses
 );
 if spell.uses == 0 {
 self.spells.remove(idx);
 }
 } else {
 println!("Not enough mana to cast {}!", spell.name);
 }
 }
}

fn main() {
 let mut merlin = Wizard::new(100);
 let fireball = Spell { name: String::from("Fireball"), cost: 10, uses: 2 };
 let ice_blast = Spell { name: String::from("Ice Blast"), cost: 15, uses: 1 };

 merlin.add_spell(fireball);
 merlin.add_spell(ice_blast);

 merlin.cast_spell("Fireball"); // Casts successfully
 merlin.cast_spell("Ice Blast"); // Casts successfully, then removed
 merlin.cast_spell("Ice Blast"); // Fails (not found)
 merlin.cast_spell("Fireball"); // Casts successfully, then removed
 merlin.cast_spell("Fireball"); // Fails (not found)
}

#[cfg(test)]
mod tests {
 use super::*;

 #[test]
 fn test_add_spell() {
 let mut wizard = Wizard::new(10);
 let spell = Spell { name: String::from("Fireball"), cost: 5, uses: 3 };
 wizard.add_spell(spell);
 assert_eq!(wizard.spells.len(), 1);
 }

 #[test]
 fn test_cast_spell() {
 let mut wizard = Wizard::new(10);
 let spell = Spell { name: String::from("Fireball"), cost: 5, uses: 3 };
 wizard.add_spell(spell);

 wizard.cast_spell("Fireball");
 assert_eq!(wizard.mana, 5);
 assert_eq!(wizard.spells.len(), 1);
 assert_eq!(wizard.spells[0].uses, 2);
 }

 #[test]
 fn test_cast_spell_insufficient_mana() {
 let mut wizard = Wizard::new(10);
 let spell = Spell { name: String::from("Fireball"), cost: 15, uses: 3 };
 wizard.add_spell(spell);

 wizard.cast_spell("Fireball");
 assert_eq!(wizard.mana, 10);
 assert_eq!(wizard.spells.len(), 1);
 assert_eq!(wizard.spells[0].uses, 3);
 }

 #[test]
 fn test_cast_spell_not_found() {
 let mut wizard = Wizard::new(10);
 wizard.cast_spell("Fireball");
 assert_eq!(wizard.mana, 10);
 }

 #[test]
 fn test_cast_spell_removal() {
 let mut wizard = Wizard::new(10);
 let spell = Spell { name: String::from("Fireball"), cost: 5, uses: 1 };
 wizard.add_spell(spell);

 wizard.cast_spell("Fireball");
 assert_eq!(wizard.mana, 5);
 assert_eq!(wizard.spells.len(), 0);
 }
}
2.5 练习：巫师的物品栏 on 编程那些事儿

2.5.1 解答

2.5.1 解答
