C# и SOLID: принципы ООП

1public class UserService
2{
3    public void CreateUser(UserDto dto) { ... }
4    public void SendEmail(string to, string body) { ... }
5    public void LogAction(string action) { ... }
6}

1public class UserService
2{
3    private readonly IUserRepository _repo;
4    private readonly IEmailService _email;
5    private readonly ILogger _logger;
6    
7    public UserService(IUserRepository repo, IEmailService email, ILogger logger)
8    {
9        _repo = repo;
10        _email = email;
11        _logger = logger;
12    }
13    
14    public async Task<User> CreateUserAsync(UserDto dto)
15    {
16        var user = new User(dto);
17        await _repo.SaveAsync(user);
18        await _email.SendAsync(dto.Email, "Welcome", "...");
19        _logger.Log("User created");
20        return user;
21    }
22}

1// ✅ Использование полиморфизма
2public interface IDiscountStrategy
3{
4    decimal Calculate(decimal price);
5}
6
7public class RegularDiscount : IDiscountStrategy
8{
9    public decimal Calculate(decimal price) => price * 0.9m;
10}
11
12public class VIPDiscount : IDiscountStrategy
13{
14    public decimal Calculate(decimal price) => price * 0.7m;
15}
16
17public class PriceCalculator
18{
19    public decimal CalculatePrice(decimal price, IDiscountStrategy strategy)
20    {
21        return strategy.Calculate(price);
22    }
23}

1// ❌ Нарушение LSP
2public class Bird
3{
4    public virtual void Fly() { ... }
5}
6
7public class Ostrich : Bird
8{
9    public override void Fly()
10    {
11        throw new NotImplementedException("Ostriches can't fly");
12    }
13}
14
15// ✅ LSP
16public interface IFlightCapable
17{
18    void Fly();
19}
20
21public class Sparrow : Bird, IFlightCapable { ... }
22public class Ostrich : Bird { ... } // Без IFlightCapable

1// ❌ Толстый интерфейс
2public interface IWorker
3{
4    void Work();
5    void Eat();
6    void Sleep();
7}
8
9// ✅ Разделённые интерфейсы
10public interface IWorkable
11{
12    void Work();
13}
14
15public interface IFeedable
16{
17    void Eat();
18}
19
20public interface ISleepable
21{
22    void Sleep();
23}
24
25public class Robot : IWorkable { ... }
26public class Human : IWorkable, IFeedable, ISleepable { ... }

1// ❌ Зависимость от конкретного класса
2public class SqlDatabase
3{
4    public void Save(string data) { ... }
5}
6
7public class UserService
8{
9    private readonly SqlDatabase _db = new SqlDatabase(); // Жёсткая связь
10}
11
12// ✅ Зависимость от абстракции
13public interface IDatabase
14{
15    void Save(string data);
16}
17
18public class UserService
19{
20    private readonly IDatabase _db;
21    
22    public UserService(IDatabase db)
23    {
24        _db = db; // Внедрение зависимости
25    }
26}