// ファクトリとして機能するメソッド
public Circle CreateCircle(CircleName circleName)
{
return(new Circle(
id,
circleName
));
}
public Circle(UserId ownerId, CircleName name)
{
if (ownerId == null)
{
throw new ArgumentNullException(nameof(ownerId));
}
if (name == null)
{
throw new ArgumentNullException(nameof(name));
}
OwnerId = ownerId;
Name = name;
}