Create IEnumerable<T>.Find()

问题

I'd like to write:

IEnumerable<Car> cars;
cars.Find(car => car.Color == "Blue")

Can I accomplish this with extension methods? The following fails because it recursively calls itself rather than calling IList.Find().

public static T Find<T>(this IEnumerable<T> list, Predicate<PermitSummary> match)
{
    return list.ToList().Find(match);
}

Thanks!

回答1:

This method already exists. It's called FirstOrDefault

cars.FirstOrDefault(car => car.Color == "Blue");

If you were to implement it yourself it would look a bit like this

public static T Find<T>(this IEnumerable<T> enumerable, Func<T,bool> predicate) {
  foreach ( var current in enumerable ) {
    if ( predicate(current) ) {
      return current;
    }
  }
  return default(T);
}

回答2:

Jared is correct if you are looking for a single blue car, any blue car will suffice. Is that what you're looking for, or are you looking for a list of blue cars?

First blue car:

Car oneCar = cars.FirstOrDefault(c => c.Color.Equals("Blue"));

List of blue cars:

IEnumerable<Car> manyCars = cars.FindAll(car => car.Color.Equals("Blue"));

回答3:

You know that Find(...) can be replaced by Where / First

IEnumerable<Car> cars;
var result = cars.Where(c => c.Color == "Blue").FirstOrDefault();

This'll return null in the event that the predicate doesn't match.

来源：https://stackoverflow.com/questions/2969643/create-ienumerablet-find