Tutorial by Examples: an

Chainable object design and chaining

Chaining and Chainable is a design methodology used to design object behaviors so that calls to object functions return references to self, or another object, providing access to additional function calls allowing the calling statement to chain together many calls without the need to reference the v...

JavaScript • Method Chaining

Steps to use custom fonts in React Native (Android)

Paste your fonts file inside android/app/src/main/assets/fonts/font_name.ttf Recompile the Android app by running react-native run-android Now, You can use fontFamily: 'font_name' in your React Native Styles

react-native • Custom Fonts

Join parent and child JSON entities using CROSS APPLY OPENJSON

Join parent objects with their child entities, for example we want a relational table of each person and their hobbies DECLARE @json nvarchar(1000) = N'[ { "id":1, "user":{"name":"John"}, "hobbies":[ {...

Microsoft SQL Server • JSON in Sql Server

Place allocation and cleanup code next to each other

Scope guards allow executing statements at certain conditions if the current block is left. import core.stdc.stdlib; void main() { int* p = cast(int*)malloc(int.sizeof); scope(exit) free(p); }

D Language • Scope guards

Unit Testing Promises with Mocha, Sinon, Chai and Proxyquire

Here we have a simple class to be tested that returns a Promise based on the results of an external ResponseProcessor that takes time to execute. For simplicty we'll assume that the processResponse method won't ever fail. import {processResponse} from '../utils/response_processor'; const ping =...

JavaScript • Unit Testing Javascript

Renamed and selective imports

Selective imports may also be renamed. void main() { import std.stdio : fooln = writeln; fooln("Hello world"); }

D Language • Imports and modules

Using move semantics on containers

You can move a container instead of copying it: void print(const std::vector<int>& vec) { for (auto&& val : vec) { std::cout << val << ", "; } std::cout << std::endl; } int main() { // initialize vec1 with 1, 2, 3, 4 and...

C++ • Move Semantics

Grant and Revoke Privileges.

Suppose, that we have three users : The Administrator of the database > admin The application with a full access for her data > read_write The read only access > read_only --ACCESS DB REVOKE CONNECT ON DATABASE nova FROM PUBLIC; GRANT CONNECT ON DATABASE nova TO user; With th...

postgresql • Role Management

Terminology and Structure

Media queries allow one to apply CSS rules based on the type of device / media (e.g. screen, print or handheld) called media type, additional aspects of the device are described with media features such as the availability of color or viewport dimensions. General Structure of a Media Query @media ...

CSS • Media Queries

Testing using setUp and tearDown function

You can set a setUp and tearDown function. A setUp function prepares your environment to tests. A tearDown function does a rollback. This is a good option when you can't modify your database and you need to create an object that simulate an object brought of database or need to init a configu...

Go • Testing

stroke (a path command)

context.stroke() Causes the perimeter of the Path to be stroked according to the current context.strokeStyle and the stroked Path is visually drawn onto the canvas. Prior to executing context.stroke (or context.fill) the Path exists in memory and is not yet visually drawn on the canvas. The unu...

html5-canvas • Path (Syntax only)

fill (a path command)

context.fill() Causes the inside of the Path to be filled according to the current context.fillStyle and the filled Path is visually drawn onto the canvas. Prior to executing context.fill (or context.stroke) the Path exists in memory and is not yet visually drawn on the canvas. Example code usi...

html5-canvas • Path (Syntax only)

clip (a path command)

context.clip Limits any future drawings to display only inside the current Path. Example: Clip this image into a triangular Path <!doctype html> <html> <head> <style> body{ background-color:white; } #canvas{border:1px solid red; } </style> <sc...

html5-canvas • Path (Syntax only)

Reduction and parallel loops

Julia provides macros to simplify distributing computation across multiple machines or workers. For instance, the following computes the sum of some number of squares, possibly in parallel. function sumofsquares(A) @parallel (+) for i in A i ^ 2 end end Usage: julia> sumo...

Julia Language • for Loops

Short-circuit operators: && and ||

For branching The short-circuiting conditional operators && and || can be used as lightweight replacements for the following constructs: x && y is equivalent to x ? y : x x || y is equivalent to x ? x : y One use for short-circuit operators is as a more concise way to test a ...

Julia Language • Conditionals

if statement with multiple branches

d = Dates.dayofweek(now()) if d == 7 println("It is Sunday!") elseif d == 6 println("It is Saturday!") elseif d == 5 println("Almost the weekend!") else println("Not the weekend yet...") end Any number of elseif branches may be used...

Julia Language • Conditionals

Installing HBase in Standalone

HBase Standalone is a mode which allow you to get rid of HDFS and to test HBase before deploying in a cluster, It is not production oriented. Installing HBase in standalone is extremely simple. First you have to download the HBase archive named hbase-X.X.X-bin.tar.gz available on one of the apache ...

hbase • Getting started with hbase

Local and application wide resources

If you only need a given resource for a specific control, you can make it more local by adding it to this specific control, instead of the window. It works exactly the same way, the only difference being that you can now only access from inside the scope of the control where you put it: <StackPa...

wpf • WPF Resources

Another Polymorphism Example

Polymorphism is one of the pillar of OOP. Poly derives from a Greek term which means 'multiple forms'. Below is an example which exhibits Polymorphism. The class Vehicle takes multiple forms as a base class. The Derived classes Ducati and Lamborghini inherits from Vehicle and overrides the base cl...

C# Language • Polymorphism

Sending events back to an activity with callback interface

If you need to send events from fragment to activity, one of the possible solutions is to define callback interface and require that the host activity implement it. Example Send callback to an activity, when fragment's button clicked First of all, define callback interface: public interface Samp...

Android • Fragments