Why not inherit from List?

Question

When planning out my programs, I often start with a chain of thought like so:

A football team is just a list of football players. Therefore, I should

Answer 1

What if the FootballTeam has a reserves team along with the main team?

class FootballTeam
{
    List Players { get; set; }
    List ReservePlayers { get; set; }
}

How would you model that with?

class FootballTeam : List 
{ 
    public string TeamName; 
    public int RunningTotal 
}

The relationship is clearly has a and not is a.

or RetiredPlayers?

class FootballTeam
{
    List Players { get; set; }
    List ReservePlayers { get; set; }
    List RetiredPlayers { get; set; }
}

As a rule of thumb, if you ever want to inherit from a collection, name the class SomethingCollection.

Does your SomethingCollection semantically make sense? Only do this if your type is a collection of Something.

In the case of FootballTeam it doesn't sound right. A Team is more than a Collection. A Team can have coaches, trainers, etc as the other answers have pointed out.

FootballCollection sounds like a collection of footballs or maybe a collection of football paraphernalia. TeamCollection, a collection of teams.

FootballPlayerCollection sounds like a collection of players which would be a valid name for a class that inherits from List if you really wanted to do that.

Really List is a perfectly good type to deal with. Maybe IList if you are returning it from a method.

In summary

Ask yourself

1. Is X a Y? or Has X a Y?

2. Do my class names mean what they are?