Tutorial by Examples: l

Basic Class Template

The basic idea of a class template is that the template parameter gets substituted by a type at compile time. The result is that the same class can be reused for multiple types. The user specifies which type will be used when a variable of the class is declared. Three examples of this are shown in m...

C++ • Templates

Simple interface

In Go, an interface is just a set of methods. We use an interface to specify a behavior of a given object. type Painter interface { Paint() } The implementing type need not declare that it is implementing the interface. It is enough to define methods of the same signature. type Rembrandt ...

Go • Interfaces

Setting up jQuery UI for the First Time Example

The jQuery UI framework helps to extend and increase the User Interface controls for jQuery JavaScript library. When you wish to use jQuery UI, you will need to add these libraries to your HTML. A quick way to start is using the Content Delivery Network available code sources: jQuery Libraries ht...

jQuery UI Library • Getting started with jQuery UI Library

Satisfy one of multiple constraints using switch

You can create a tuple and use a switch like so: var str: String? = "hi" var x: Int? = 5 switch (str, x) { case (.Some,.Some): print("Both have values") case (.Some, nil): print("String has a value") case (nil, .Some): print("Int has a value&...

Swift Language • Switch

Using a context processor to access your most recent blog entries in all templates

Assuming you have a model called Post defined in your models.py file that contains blog posts, and has a date_published field. Step 1: Write the context processor Create (or add to) a file in your app directory called context_processors.py: from myapp.models import Post def recent_blog_posts...

Django • Context Processors

Why use Default Methods?

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...

Java Language • Default Methods

Speeding tough-to-vectorize for loops by byte compiling

Following the Rcpp example in this documentation entry, consider the following tough-to-vectorize function, which creates a vector of length len where the first element is specified (first) and each element x_i is equal to cos(x_{i-1} + 1): repeatedCosPlusOne <- function(first, len) { x <-...

R Language • Speeding up tough-to-vectorize code

Creating a model with relationships

Many-to-One Relationship from django.db import models class Author(models.Model): name = models.CharField(max_length=50) #Book has a foreignkey (many to one) relationship with author class Book(models.Model): author = models.ForeignKey(Author, on_delete=models.CASCADE) publish_...

Django • Models

jQuery UI Sortable - Drop Placeholder

This example of the Sortable using a Placeholder is common usage. Sortable is applied to a group of DOM elements, allowing the user to move items around in the list via Drag'n Drop style actions. <!doctype html> <html lang="en"> <head> <meta charset="utf-8&q...

jQuery UI Library • jquery ui sortable

Roots: nth-root with fractional exponents

While the math.sqrt function is provided for the specific case of square roots, it's often convenient to use the exponentiation operator (**) with fractional exponents to perform nth-root operations, like cube roots. The inverse of an exponentiation is exponentiation by the exponent's reciprocal. S...

Python Language • Exponentiation

Using modules from other program units

To access entities declared in a module from another program unit (module, procedure or program), the module must be used with the use statement. module shared_data implicit none integer :: iarray(4) = [1, 2, 3, 4] real :: rarray(4) = [1., 2., 3., 4.] end module program test !...

Fortran • Usage of Modules

A basic unmanaged table.

At some point in your use of Django, you may find yourself wanting to interact with tables which have already been created, or with database views. In these cases, you would not want Django to manage the tables through its migrations. To set this up, you need to add only one variable to your model's...

Django • Models

Format literals (f-string)

Literal format strings were introduced in PEP 498 (Python3.6 and upwards), allowing you to prepend f to the beginning of a string literal to effectively apply .format to it with all variables in the current scope. >>> foo = 'bar' >>> f'Foo is {foo}' 'Foo is bar' This works wi...

Python Language • String Formatting

Simple text input widget

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'

Django • Form Widgets

Logging to Syslog service

It is possible to configure Django to output log to a local or remote syslog service. This configuration uses the python builtin SysLogHandler. from logging.handlers import SysLogHandler LOGGING = { 'version': 1, 'disable_existing_loggers': True, 'formatters': { 'standard':...

Django • Logging

Testing - a complete example

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...

Django • Unit Testing

Installation or Setup

Detailed instructions on getting couchbase set up or installed.

couchbase • Getting started with couchbase

Call constructor

Getting the Constructor Object You can obtain Constructor class from the Class object like this: Class myClass = ... // get a class object Constructor[] constructors = myClass.getConstructors(); Where the constructors variable will have one Constructor instance for each public constructor decl...

Java Language • Reflection API

Using custom deleters to create a wrapper to a C interface

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...

C++ • Smart Pointers

Writing a lens without Template Haskell

To demystify Template Haskell, suppose you have data Example a = Example { _foo :: Int, _bar :: a } then makeLenses 'Example produces (more or less) foo :: Lens' (Example a) Int bar :: Lens (Example a) (Example b) a b There's nothing particularly magical going on, though. You can write ...

Haskell Language • Lens