Code shared from the Rust Playground

playground.rs

pub struct Monster {
    hp: u8, // health points
    sp: u8, // spell points
    
    friends: Vec<Friend>,
}

pub struct Friend {
    loyalty: u8,
}




impl Monster {
    pub fn final_breath(&mut self) {
    
    
        self.heal();
        
        println!("Healing for {}", self.hp);
    
    }
    
    pub fn heal(&mut self) {
        for f in self.friends.iter_mut(){
            
            self.hp += f.loyalty;
            self.sp -= f.loyalty;
            
        }
    }
    

   
}



// pub struct Monster {
//     hp: u8, // health points
//     sp: u8, // spell points
//     friends: Vec<Friend>,
// }

// pub struct Friend {
//     loyalty: u8,
// }




// impl Monster {
//     pub fn final_breath(&mut self) {
        
//         if let Some(friend) = self.friends.first() {
        
//             self.heal(friend.loyalty);
//             println!("Healing for {}", friend.loyalty);
            
//         }
    
//     }
    

//     fn heal(&mut self, amount: u8) {
//         self.hp += amount;
//         self.sp -= amount;
//     }
// }



// warning: cannot borrow `*self` as mutable because it is also borrowed as immutable
//   --> src/main.rs:33:9
//   |
// 31 |         let friend = self.friends.first().unwrap();
//   |                      ------------ immutable borrow occurs here
// 32 |         
// 33 |         self.heal(friend.loyalty);
//   |         ^^^^      -------------- immutable borrow later used here
//   |         |
//   |         mutable borrow occurs here
//   |
//   = note: `#[warn(mutable_borrow_reservation_conflict)]` on by default
//   = warning: this borrowing pattern was not meant to be accepted, and may become a hard error in the future
//   = note: for more information, see issue #59159 <https://github.com/rust-lang/rust/issues/59159>

// impl Monster {
//     pub fn final_breath(&mut self) {
    
//         // Error 
//         // if let Some(friend) = self.friends.first() {
        
//         //     self.heal(friend.loyalty);
//         //     println!("Healing for {}", friend.loyalty);
            
//         // }
    
//         self.change_heal();
//         self.display_heal();
        
       
//     }
    
    
//     fn change_heal(&mut self){
    
//         let friend = self.friends.first();
        
//         self.heal(friend.loyalty);
    
        
        
//         // if let Some(friend) = self.friends.first() {
        
//         //     self.heal(friend.loyalty);
            
//         // }
//     }
    
    
//     fn display_heal(&self){
//         if let Some(friend) = self.friends.first() {
            
//             println!("Healing for {}", friend.loyalty);
            
//         }
//     }

//     fn heal(&mut self, amount: u8) {
//         self.hp += amount;
//         self.sp -= amount;
//     }
// }

fn main() {}