Tutorial by Examples: et

The simple answer is that it allows you to evolve an existing interface without breaking existing implementations. For example, you have Swim interface that you published 20 years ago. public interface Swim { void backStroke(); } We did a great job, our interface is very popular, there ar...

The most simple example of widget is custom text input. For instance, to create an <input type="tel">, you have to subclass TextInput and set input_type to 'tel'. from django.forms.widgets import TextInput class PhoneInput(TextInput): input_type = 'tel'

You can create widgets composed of multiple widgets using MultiWidget. from datetime import date from django.forms.widgets import MultiWidget, Select from django.utils.dates import MONTHS class SelectMonthDateWidget(MultiWidget): """This widget allows the user to fill in ...

This assumes that you have read the documentation about starting a new Django project. Let us assume that the main app in your project is named td (short for test driven). To create your first test, create a file named test_view.py and copy paste the following content into it. from django.test impo...

Detailed instructions on getting couchbase set up or installed.

Many C interfaces such as SDL2 have their own deletion functions. This means that you cannot use smart pointers directly: std::unique_ptr<SDL_Surface> a; // won't work, UNSAFE! Instead, you need to define your own deleter. The examples here use the SDL_Surface structure which should be fre...

This type of tests make sure that your code compiles properly and will appear in the generated documentation for your project. In addition to that, the example tests can assert that your test produces proper output. sum.go: package sum // Sum calculates the sum of two integers func Sum(a, b in...

Create a new playground file: First option: From Xcode welcome screen, select the first option (Get started with a playground). Second option: From menu select File → New → Playground (⌥⇧⌘N). Name your playground and select the platform (iOS/macOS/tvOS), then click Next. ...

public IEnumerable<int> F1() { for (int i = 0; i < 3; i++) yield return i; //return F2(); // Compile Error!! foreach (var element in F2()) yield return element; } public int[] F2() { return new[] { 3, 4, 5 }; }

OptionSetType is a protocol designed to represent bit mask types where individual bits represent members of the set. A set of logical and/or functions enforce the proper syntax: struct Features : OptionSet { let rawValue : Int static let none = Features(rawValue: 0) static let feature0 = F...

function sayHello(name) print("Hello, " .. name .. "!") end That function is a simple function, and it works well. But what would happen if we just called sayHello()? stdin:2: attempt to concatenate local 'name' (a nil value) stack traceback: stdin:2: in function ...

Instance methods are functions that belong to instances of a type in Swift (a class, struct, enumeration, or protocol). Type methods are called on a type itself. Instance Methods Instance methods are defined with a func declaration inside the definition of the type, or in an extension. class Coun...

home_url() is used for retrieving the current site home url. <?php echo esc_url( home_url( '/' ) ) ); ?> Output http://www.example.com

You can delete data after writing it to the database. You can either delete a model instance if you have retrieved one, or specify conditions for which records to delete. To delete a model instance, retrieve it and call the delete() method: $user = User::find(1); $user->delete(); Alternat...

Implementations in classes, including abstract declarations, take precedence over all interface defaults. Abstract class method takes precedence over Interface Default Method. public interface Swim { default void backStroke() { System.out.println("Swim.backStroke"); ...

Macros return code. Since code in Lisp consists of lists, one can use the regular list manipulation functions to generate it. ;; A pointless macro (defmacro echo (form) (list 'progn (list 'format t "Form: ~a~%" (list 'quote form)) form)) This is often very hard to...

Multiple transforms can be applied to an element in one property like this: transform: rotate(15deg) translateX(200px); This will rotate the element 15 degrees clockwise and then translate it 200px to the right. In chained transforms, the coordinate system moves with the element. This means tha...

h2 { /* adds a 1px space horizontally between each letter; also known as tracking */ letter-spacing: 1px; } The letter-spacing property is used to specify the space between the characters in a text. ! letter-spacing also supports negative values: p { letter-spacing: -1px; }...

With Git, you can (almost) always turn the clock back Don't be afraid to experiment with commands that rewrite history*. Git doesn't delete your commits for 90 days by default, and during that time you can easily recover them from the reflog: $ git reset @~3 # go back 3 commits $ git reflog c4...

git diff 1234abc..6789def # old new E.g.: Show the changes made in the last 3 commits: git diff @~3..@ # HEAD -3 HEAD Note: the two dots (..) is optional, but adds clarity. This will show the textual difference between the commits, regardless of where they are in the tree.