Tutorial by Examples: u

Testing NULLs

IS NULL / IS NOT NULL -- = NULL does not work like you expect. x <=> y is a "null-safe" comparison. In a LEFT JOIN tests for rows of a for which there is not a corresponding row in b. SELECT ... FROM a LEFT JOIN b ON ... WHERE b.id IS NULL
MySQL • NULL

Atomic Add Function

int fakeMalloc(__local int * addrCounter,int size) { // lock addrCounter // adds size to addrCounter's pointed cell value // unlock // return old value of addrCounter's pointed cell // serial between all threads visiting -> slow ret...

Using GSON with inheritance

GSON does not support inheritance our of the box. Let's say we have the following class hierarchy: public class BaseClass { int a; public int getInt() { return a; } } public class DerivedClass1 extends BaseClass { int b; @Override public int getIn...

Basic Account Authenticator Service

The Android Account Authenticator system can be used to make the client authenticate with a remote server. Three pieces of information are required: A service, triggered by the android.accounts.AccountAuthenticator. Its onBind method should return a subclass of AbstractAccountAuthenticator. An a...

Directory Structure

The standard structure for a project built by SBT is: projectName/ build.sbt project/ <SBT sub-build information> src/ main/ scala/ <Scala source files> java/ <Java source files> resources/ ...

Inspect HTML Structure

On a desktop version of Chrome, the contents of the page can be inspected. This shows the document object model (DOM) of the HTML, the Cascading Style Sheet styles (CSS), and much more. Enter inspection by one of many options: Right click on a web page, and select Inspect From the Chrome Menu, ...

Product Collection

$ProductCollection=Mage::getModel('catalog/product')->getCollection(); Selecting the specific Attribute $ProductCollection->addAttributeToSelect(array('name', 'product_url', 'small_image')); Selecting the All Attribute $ProductCollection->addAttributeToSelect('*'); Add Filter on ...

Introduction to Metaclasses

What is a metaclass? In Python, everything is an object: integers, strings, lists, even functions and classes themselves are objects. And every object is an instance of a class. To check the class of an object x, one can call type(x), so: >>> type(5) <type 'int'> >>> typ...

The default metaclass

You may have heard that everything in Python is an object. It is true, and all objects have a class: >>> type(1) int The literal 1 is an instance of int. Lets declare a class: >>> class Foo(object): ... pass ... Now lets instantiate it: >>> bar = Foo() Wh...

Changing text color using switch condition

Let's assume we have an entity status field with 3 options Tentative Pending Approved Our goal is to show different color for each status as follow: Tentative will be Red Pending will be Orange Approved will be Green The switch condition: =Switch(Fields!ItemStatus.Value = "Tentativ...

Iterating over members of a struct/class without their inherited members

module main; auto getMemberNames(T)() @safe pure { string[] members; foreach (derived; __traits(derivedMembers, T)) { members ~= derived; } return members; } class Foo { int a; int b; } class Bar : Foo { int c; int d; int e...

Declare dependencies for build types

Dependencies can be added for specific Build types: android { ... buildTypes { release { //... } debug { //.... } } } dependencies { debugCompile 'com.android.support:appcompat-v7:24.1.1' releaseCompile ...

Introduction

Template Literals act like strings with special features. They are enclosed by by the back-tick `` and can be spanned across multiple lines. Template Literals can contain embedded expressions too. These expressions are indicated by a $ sign and curly braces {} //A single line Template Literal v...

Custom Styled Map

<!DOCTYPE html> <html> <head> <title>Styled Maps</title> <meta charset="utf-8"> <style> #map { height: 100%; } </style> </head> <body> <div id="map"></div> <script type="t...

Compiling on Linux

To compile a PHP extension in a typical Linux environment, there are a few pre-requisites: Basic Unix skills (being able to operate "make" and a C compiler) An ANSI C compiler The source code for the PHP extension you want to compile Generally there are two ways to compile a PHP ex...

Producers

A Producer is some monadic action that can yield values for downstream consumption: type Producer b = Proxy X () () b yield :: Monad m => a -> Producer a m () For example: naturals :: Monad m => Producer Int m () naturals = each [1..] -- each is a utility function exported by Pipes ...

Consumers

A Consumer can only await values from upstream. type Consumer a = Proxy () a () X await :: Monad m => Consumer a m a For example: fancyPrint :: MonadIO m => Consumer String m () fancyPrint = forever $ do numStr <- await liftIO $ putStrLn ("I received: " ++ numStr) ...

Running Pipes with runEffect

We use runEffect to run our Pipe: main :: IO () main = do runEffect $ naturalsUntil 10 >-> intToStr >-> fancyPrint Note that runEffect requires an Effect, which is a self-contained Proxy with no inputs or outputs: runEffect :: Monad m => Effect m r -> m r type Effect = Pr...

Run script in debug mode

To run script in debug mode you should add -d option in the command line: $perl -d script.pl If t is specified, it indicates to the debugger that threads will be used in the code being debugged: $perl -dt script.pl Additional info at perldocperlrun

Getting Instance of Unsafe

Unsafe is stored as a private field that cannot be accessed directly. The constructor is private and the only method to access public static Unsafe getUnsafe() has privileged access. By use of reflection, there is a work-around to make private fields accessible: public static final Unsafe UNSAFE; ...

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