Extension method, Func of T and List of T

Question

I would like to code a function that can accomplish some check before insert a value into a List. For example:

class Person {
    public string Name { get; set; }
    public int Value { get; set; }
    public Guid Id { get; set; }
}
-------
var persons = new List<Person>();
// add a new person if John doesn't exist
persons.AddIf(s => !s.Name.Equals("John"), new Person { ... });
----
public static void AddIf(this List<T> lst, Func<T, bool> check, T data)
{
     // how can I use the Func 'check' to check if exist an object with the
     // information that the client wrote and, if not exists, insert the new value
     // into the list???
     if ( check )
}

How can I use the Func 'check' to check if exist an object with the information that the client wrote and, if not exists, insert the new value into the list?

Answer 1

You need to make your method generic.

public static void AddIf<T>(this List<T> lst, Func<T, bool> check, T data)
{
    if (!lst.All(check))
        return;

    lst.Add(data);
}

And usage like you wanted (all items should satisfy predicate):

persons.AddIf(s => !s.Name.Equals("John"), new Person { ... });