How do i return IEnumerable<T> from a method

Question

I am developing Interface for a sample project i wanted it to be as generic as possible so i created a interface like below

public interface IUserFactory
{    
    IEnumerable<Users> GetAll();
    Users GetOne(int Id);
}

but then it happened i had to duplicate the interface to do below

public interface IProjectFactory
{    
    IEnumerable<Projects> GetAll(User user);
    Project GetOne(int Id);
}

if you looked at above difference is just types they return, so i created something like below only to find i get error Cannot Resolve Symbol T What am i doing wrong

public interface IFactory
{    
    IEnumerable<T> GetAll();
    T GetOne(int Id);
}

Answer 1

You need to use a generic interface/class, not just generic methods:

public interface IFactory<T>
{    
    IEnumerable<T> GetAll();
    T GetOne(int Id);
}

Defining a generic type on the interface/class ensures the type is known throughout the class (wherever the type specifier is used).