It’s “just sugarcoating” for readability, but they do have common meanings: Methods ending in ! perform some permanent or potentially dangerous change; for example: Enumerable#sort returns a sorted version of the object while Enumerable#sort! sorts it in place. In Rails, ActiveRecord::Base#save returns false if saving failed, while ActiveRecord::Base#save! raises an exception. Kernel::exit causes a script … Read more
Javascript is single threaded, hence the page blocking behaviour. You can use the deferred/promise approach suggested by others. The most basic way would be to use window.setTimeout. E.g. function checkFlag() { if(flag === false) { window.setTimeout(checkFlag, 100); /* this checks the flag every 100 milliseconds*/ } else { /* do something*/ } } checkFlag(); Here … Read more
Predicate: essentially Func<T, bool>; asks the question “does the specified argument satisfy the condition represented by the delegate?” Used in things like List.FindAll. Action: Perform an action given the arguments. Very general purpose. Not used much in LINQ as it implies side-effects, basically. Func: Used extensively in LINQ, usually to transform the argument, e.g. by … Read more
There are no built-in always-true and always-false predicates in Java 8. The most concise way to write these is x -> true and x -> false Compare these to Predicates.alwaysTrue() // Guava and finally to an anonymous inner class: new Predicate<Object>() { public boolean test(Object x) { return true; } } Probably the reason that … Read more
Predicate<T> is a functional construct providing a convenient way of basically testing if something is true of a given T object. For example suppose I have a class: class Person { public string Name { get; set; } public int Age { get; set; } } Now let’s say I have a List<Person> people and … Read more
Would the dynamic linq library help here? In particular, I’m thinking as a Where clause. If necessary, put it inside a list/array just to call .Where(string) on it! i.e. var people = new List<Person> { person }; int match = people.Where(filter).Any(); If not, writing a parser (using Expression under the hood) isn’t hugely taxing – … Read more
While Predicate has been introduced at the same time that List<T> and Array<T>, in .net 2.0, the different Func and Action variants come from .net 3.5. So those Func predicates are used mainly for consistency in the LINQ operators. As of .net 3.5, about using Func<T> and Action<T> the guideline states: Do use the new … Read more
To find the first element in a sequence seq that matches a predicate: next(x for x in seq if predicate(x)) Or simply: Python 2: next(itertools.ifilter(predicate, seq)) Python 3: next(filter(predicate, seq)) These will raise a StopIteration exception if the predicate does not match for any element. To return None if there is no such element: next((x … Read more
A predicate is a function that returns true or false. A predicate delegate is a reference to a predicate. So basically a predicate delegate is a reference to a function that returns true or false. Predicates are very useful for filtering a list of values – here is an example. using System; using System.Collections.Generic; class … Read more
Predicate.not( … ) java-11 offers a new method Predicate#not So you can negate the method reference: Stream<String> s = …; long nonEmptyStrings = s.filter(Predicate.not(String::isEmpty)).count();