Tutorial by Examples: b

Base Document Language

It’s a good practice to declare the primary language of the document in the html element: <html lang="en"> If no other lang attribute is specified in the document, it means that everything (i.e., element content and attribute text values) is in that language. If the document con...

HTML • Content Languages

Recurse into a subpattern

You can recurse into a subpattern using the following constructs (depending on the flavor), assuming n is a capturing group number, and name the name of a capturing group. (?n) \g<n> \g'0' (?&name) \g<name> \g'name' (?P>name) The following pattern: \[(?<angle>&...

Regular Expressions • Recursion

Subpattern definitions

The (?(DEFINE)...) construct lets you define subpatterns you may reference later through recursion. When encountered in the pattern it will not be matched against. This group should contain named subpattern definitions, which will be accessible only through recursion. You can define grammars this w...

Regular Expressions • Recursion

Using the Delegate Pattern (passing data back)

To pass data from the current view controller back to the previous view controller, you can use the delegate pattern. This example assumes that you have made a segue in the Interface Builder and that you set the segue identifier to showSecondViewController. The outlets and actions must also be ho...

iOS • Passing Data between View Controllers

Verbatim strings instruct the compiler to not use character escapes

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 ...

C# Language • Verbatim Strings

Using built-in functions as callbacks

In functions taking callable as an argument, you can also put a string with PHP built-in function. It's common to use trim as array_map parameter to remove leading and trailing whitespace from all strings in the array. $arr = [' one ', 'two ', ' three']; var_dump(array_map('trim', $arr)); ...

PHP • Functional Programming

recursively enumerating a subtree

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, ...

SQL • Common Table Expressions

Define and use Build Configuration Fields

BuildConfigField Gradle allows buildConfigField lines to define constants. These constants will be accessible at runtime as static fields of the BuildConfig class. This can be used to create flavors by defining all fields within the defaultConfig block, then overriding them for individual build fla...

Android • Gradle for Android

Create a swarm on Linux using docker-machine and VirtualBox

# 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...

Docker • Docker swarm mode

Bitwise NOT

The ~ operator will flip all of the bits in the number. Since computers use signed number representations — most notably, the two's complement notation to encode negative binary numbers where negative numbers are written with a leading one (1) instead of a leading zero (0). This means that if you w...

Python Language • Bitwise Operators

Lambdas can be emitted both as `Func` and `Expression`

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...

C# Language • Lambda expressions

Counting the elements of a Foldable structure

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) ...

Haskell Language • Foldable

An instance of Foldable for a binary tree

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...

Haskell Language • Foldable

Instantiating Functor and Foldable for a Traversable structure

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 ...

Haskell Language • Traversable

An instance of Traversable for a binary tree

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 <*...

Haskell Language • Traversable

vector: The Exception To So Many, So Many Rules

The standard (section 23.3.7) specifies that a specialization of vector<bool> is provided, which optimizes space by packing the bool values, so that each takes up only one bit. Since bits aren't addressable in C++, this means that several requirements on vector are not placed on vector<bool...

C++ • std::vector

Defining and Undefining Symbols

A compiler symbol is a keyword that is defined at compile-time that can be checked for to conditionally execute specific sections of code. There are three ways to define a compiler symbol. They can be defined via code: #define MYSYMBOL They can be defined in Visual Studio, under Project Propert...

C# Language • Preprocessor directives

Region Blocks

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...

C# Language • Preprocessor directives

Using Ajax to Submit a Form

Sometimes you may have a form and want to submit it using ajax. Suppose you have this simple form - <form id="ajax_form" action="form_action.php"> <label for="name">Name :</label> <input name="name" id="name" type="t...

jQuery • Ajax

Reading an uninitialized object that is not backed by memory

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...

C Language • Undefined behavior