Tutorial by Examples: d

In most scripting languages, if a function call fails, it may throw an exception and stop execution of the program. Bash commands do not have exceptions, but they do have exit codes. A non-zero exit code signals failure, however, a non-zero exit code will not stop execution of the program. This can...

The behaviour of virtual functions in constructors and destructors is often confusing when first encountered. #include <iostream> using namespace std; class base { public: base() { f("base constructor"); } ~base() { f("base destructor"); } virtual co...

Principal Component Analysis finds sequences of linear combinations of the features. The first linear combination maximizes the variance of the features (subject to a unit constraint). Each of the following linear combinations maximizes the variance of the features in the subspace orthogonal to that...

Security is a very general, broad field, and touches every aspect of development, deployment, support, among other areas. Per the (ISC)2, there are 10 domains, and include Physical security, in addition to the "Software" aspects. The intent of information security is to protect the confid...

We can use the class DateInterval to add or subtract some interval in a DateTime object. See the example below, where we are adding an interval of 7 days and printing a message on the screen: $now = new DateTime();// empty argument returns the current date $interval = new DateInterval('P7D');//th...

Learning the parameters of a prediction function and testing it on the same data is a methodological mistake: a model that would just repeat the labels of the samples that it has just seen would have a perfect score but would fail to predict anything useful on yet-unseen data. This situation is call...

Standard DateTime Formatting DateTimeForma­tInfo specifies a set of specifiers for simple date and time formating. Every specifier correspond to a particular DateTimeFormatInfo format pattern. //Create datetime DateTime dt = new DateTime(2016,08,01,18,50,23,230); var t = String.Format("{0...

Any nullable type is a generic type. And any nullable type is a value type. There are some tricks which allow to effectively use the result of the Nullable.GetUnderlyingType method when creating code related to reflection/code-generation purposes: public static class TypesHelper { public stat...

const CACHE_TAG_NAMESPACE_MODULE = "YOUR_MODULES_CACHE_TAGS"; $cacheGroup = 'namespace_module'; $useCache = Mage::app()->useCache($cacheGroup); if (true === $useCache) { $cacheId = 'unique_name'; if ($cacheContent = Mage::app()->loadCache($cacheId)) { $html ...

Mage::app()->removeCache($cacheId); Flush all Magento cache entries Mage::app()->cleanCache() or: Mage::app()->getCacheInstance()->flush();

Redis configuration: Install redis (2.4+ required) Install phpredis Install the Magento extension Cm_Cache_Backend_Redis (only for Magento 1.7 and below) Edit your app/etc/local.xml: <global> ... <cache> <backend>Cm_Cache_Backend_Redis</backend> <b...

NSArray *a = @[@1]; a = [a arrayByAddingObject:@2]; a = [a arrayByAddingObjectsFromArray:@[@3, @4, @5]]; These methods are optimized to recreate the new array very efficiently, usually without having to destroy the original array or even allocate more memory.

public class Producer { private static Random random = new Random((int)DateTime.UtcNow.Ticks); //produce the value that will be posted to buffer block public double Produce ( ) { var value = random.NextDouble(); Console.WriteLine($"Producing value: {value}...

The addition and multiplication have equivalents in this type algebra. They correspond to the tagged unions and product types. data Sum a b = A a | B b data Prod a b = Prod a b We can see how the number of inhabitants of every type corresponds to the operations of the algebra. Equivalently, we...

The derivative of a type is the type of its type of one-hole contexts. This is the type that we would get if we make a type variable disappear in every possible point and sum the results. As an example, we can take the triple type (a,a,a), and derive it, obtaining data OneHoleContextsOfTriple = (a...

The auto keyword by itself represents a value type, similar to int or char. It can be modified with the const keyword and the & symbol to represent a const type or a reference type, respectively. These modifiers can be combined. In this example, s is a value type (its type will be inferred as s...

Usage Sometimes, you could have to debug code in another PhpStorm project, you have to update the configuration. PHP configuration In php.ini, edit file and put xdebug.remote_autostart = 1 PhpStorm configuration You also have to configure your IDE: In the phpStorm configuration, Max. sim...

The most important consequence of the One Definition Rule is that non-inline functions with external linkage should only be defined once in a program, although they can be declared multiple times. Therefore, such functions should not be defined in headers, since a header can be included multiple tim...

Lets use the same code as above for this example. #include <iostream> void fail() { int *p1; int *p2(NULL); int *p3 = p1; if (p3) { std::cout << *p2 << std::endl; } } int main() { fail(); } First lets compile it g++ -g -o main m...

A function template can be overloaded under the rules for non-template function overloading (same name, but different parameter types) and in addition to that, the overloading is valid if The return type is different, or The template parameter list is different, except for the naming of paramete...