Tutorial by Examples: re

A reference cycle (or retain cycle) is so named because it indicates a cycle in the object graph: Each arrow indicates one object retaining another (a strong reference). Unless the cycle is broken, the memory for these objects will never be freed. A retain cycle is created when two instances of ...

In a normal string, the backslash character is the escape character, which instructs the compiler to look at the next character(s) to determine the actual character in the string. (Full list of character escapes) In verbatim strings, there are no character escapes (except for "" which is ...

WITH RECURSIVE ManagersOfJonathon AS ( -- start with this row SELECT * FROM Employees WHERE ID = 4 UNION ALL -- get manager(s) of all previously selected rows SELECT Employees.* FROM Employees JOIN ManagersOfJonathon ON Employees.ID = Manager...

WITH RECURSIVE ManagedByJames(Level, ID, FName, LName) AS ( -- start with this row SELECT 1, ID, FName, LName FROM Employees WHERE ID = 1 UNION ALL -- get employees that have any of the previously selected rows as manager SELECT ManagedByJames.Level + 1, ...

# Create the nodes # In a real world scenario we would use at least 3 managers to cover the fail of one manager. docker-machine create -d virtualbox manager docker-machine create -d virtualbox worker1 # Create the swarm # It is possible to define a port for the *advertise-addr* and *listen-ad...

Assuming the following Person class: public class Person { public string Name { get; set; } public int Age { get; set; } } The following lambda: p => p.Age > 18 Can be passed as an argument to both methods: public void AsFunc(Func<Person, bool> func) public void AsE...

<input type="reset" value="Reset"> An input of type reset creates a button which, when clicked, resets all inputs in the form it is contained in to their default state. Text in an input field will be reset to blank or its default value (specified using the value attri...

length counts the occurences of elements a in a foldable structure t a. ghci> length [7, 2, 9] -- t ~ [] 3 ghci> length (Right 'a') -- t ~ Either e 1 -- 'Either e a' may contain zero or one 'a' ghci> length (Left "foo") -- t ~ Either String 0 ghci> length (3, True) ...

Any fold can be run in the opposite direction with the help of the Dual monoid, which flips an existing monoid so that aggregation goes backwards. newtype Dual a = Dual { getDual :: a } instance Monoid m => Monoid (Dual m) where mempty = Dual mempty (Dual x) `mappend` (Dual y) = Dua...

To instantiate Foldable you need to provide a definition for at least foldMap or foldr. data Tree a = Leaf | Node (Tree a) a (Tree a) instance Foldable Tree where foldMap f Leaf = mempty foldMap f (Node l x r) = foldMap f l `mappend` f x `mappend` foldMap f r fo...

import Data.Traversable as Traversable data MyType a = -- ... instance Traversable MyType where traverse = -- ... Every Traversable structure can be made a Foldable Functor using the fmapDefault and foldMapDefault functions found in Data.Traversable. instance Functor MyType where ...

Implementations of traverse usually look like an implementation of fmap lifted into an Applicative context. data Tree a = Leaf | Node (Tree a) a (Tree a) instance Traversable Tree where traverse f Leaf = pure Leaf traverse f (Node l x r) = Node <$> traverse f l <*...

A traversal can be run in the opposite direction with the help of the Backwards applicative functor, which flips an existing applicative so that composed effects take place in reversed order. newtype Backwards f a = Backwards { forwards :: f a } instance Applicative f => Applicative (Backward...

When the following is compiled, it will return a different value depending on which directives are defined. // Compile with /d:A or /d:B to see the difference string SomeFunction() { #if A return "A"; #elif B return "B"; #else return "C"; #endif ...

Use #region and #endregion to define a collapsible code region. #region Event Handlers public void Button_Click(object s, EventArgs e) { // ... } public void DropDown_SelectedIndexChanged(object s, EventArgs e) { // ... } #endregion These directives are only beneficial whe...

#import <Foundation/Foundation.h> @interface Car:NSObject { NSString *CarMotorCode; NSString *CarChassisCode; } - (instancetype)initWithMotorValue:(NSString *) motorCode andChassisValue:(NSInteger)chassisCode; - (void) startCar; - (void) stopCar; @end @implementation Car...

C11 Reading an object will cause undefined behavior, if the object is1: uninitialized defined with automatic storage duration it's address is never taken The variable a in the below example satisfies all those conditions: void Function( void ) { int a; int b = a; } 1 (Quo...

Array types inherit their equals() (and hashCode()) implementations from java.lang.Object, so equals() will only return true when comparing against the exact same array object. To compare arrays for equality based on their values, use java.util.Arrays.equals, which is overloaded for all array types...

// Convert string to ArrayBuffer. This step is only necessary if you wish to hash a string, not if you aready got an ArrayBuffer such as an Uint8Array. var input = new TextEncoder('utf-8').encode('Hello world!'); // Calculate the SHA-256 digest crypto.subtle.digest('SHA-256', input) // Wait fo...

6 var myIterableObject = {}; // An Iterable object must define a method located at the Symbol.iterator key: myIterableObject[Symbol.iterator] = function () { // The iterator should return an Iterator object return { // The Iterator object must implement a method, next() next: func...