predicate

If I wrote the Predicate interface, I'd want to encode in the interface the fact that it's just a function that returns a primitive boolean , like this: @FunctionalInterface public interface Predicate<T> extends Function<T, Boolean> { boolean test(T t); @Override default Boolean apply(T t) { return Boolean.valueOf(test(t)); } } I was wondering, is there a compelling reason Java 8 API designers chose to keep the Predicate completely separate from Function ? Is there some evidence that they considered doing so and decided against it? I guess similar question goes for all the other 'special'

After looking on MSDN, it's still unclear to me how I should form a proper predicate to use the Find() method in List using a member variable of T (where T is a class) For example: public class Car { public string Make; public string Model; public int Year; } { // somewhere in my code List<Car> carList = new List<Car>(); // ... code to add Cars ... Car myCar = new Car(); // Find the first of each car made between 1980 and 2000 for (int x = 1980; x < 2000; x++) { myCar = carList.Find(byYear(x)); Console.Writeline(myCar.Make + myCar.Model); } } What should my "byYear" predicate look like? (The

I have a method that accepts an Expression<Func<T, bool>> as a parameter. I would like to use it as a predicate in the List.Find() method, but I can't seem to convert it to a Predicate which List takes. Do you know a simple way to do this? public IList<T> Find<T>(Expression<Func<T, bool>> expression) where T : class, new() { var list = GetList<T>(); var predicate = [what goes here to convert expression?]; return list.Find(predicate); } Update Combining answers from tvanfosson and 280Z28, I am now using this: public IList<T> Find<T>(Expression<Func<T, bool>> expression) where T : class, new() {

I am fetching a set of objects from a Core Data persistent store using a fetch request and a predicate. My current predicate simply checks whether an attribute is >= a certain value. This all works great, except that I want to finally exclude any objects that are currently held in an array. I basically need to be able to exclude a set of objects, and the only way I think I can do this is to be able to get a list of objectID from my managed objects array, and create another expression in my predicate to ensure that any objects returned don't have the same objectID . I.E. @"ANY records.objectID

Functions such as std::find_if from the algorithm header are really useful, but 1 serious limit for me is the fact that I can only use 1 predicate for each call to count_if . For example given a container like an std::vector I would like to apply, at the same time, with the same iteration of find_if , multiple predicates; there is something in the standard library that makes this possible while keeping this functional approach ? Just combine them with a lambda: std::find_if(begin(vec), end(vec), [](elem_t val) { return f1(val) || f2(val); }); 来源： https://stackoverflow.com/questions/20754848

I have a cloudkit record with 5 fields: Active User1 User2 User3 User4 I am trying to pick the record where one of the 4 user fields match with the userID variable. Only one other the 4 user fields will match the userID variable. This is the code I am using: var userID = "0984093843897" predicate = NSPredicate(format: "userID1 = %@ OR userID2 = %@ OR userID3 = %@ OR userID4 = %@ AND active = %@", userID, userID, userID, userID, true) Basically what I am trying to achieve is something similar to the statement bellow: if userID1 == userID || userID2 == userID || userID3 == userID || userID4 ==