yield_return_example_2.cs

class Person
{
    public int Age { get; }
    public string Name { get; }
    
    public Person(int age, string name)
    {
        this.Age = age;
        this.Name = name;
    }
    
    public override string ToString()
    {
        return $"{ Name }: { Age }";
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        InstanceSubsetExampe();
    }

    private static void InstanceSubsetExampe()
    {
        var persons = new List<Person>() 
          { 
            new Person(15, "Carl"), 
            new Person(20, "Dan"), 
            new Person(25, "Mitchell") 
          };
        
        foreach (var adultPerson in GetAdults(persons))
        {
            Console.WriteLine(adultPerson);
        }
    }
    
    private static IEnumerable<Person> GetAdults(IEnumerable<Person> persons)
    {
        foreach (var person in persons)
        {
            if(person.Age >= 18)
            {
                yield return person;
            }
        }
    }
}