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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...

Detailed instructions on getting database-design set up or installed.

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...

C-style bit-manipulation template <typename T> T rightmostSetBitRemoved(T n) { // static_assert(std::is_integral<T>::value && !std::is_signed<T>::value, "type should be unsigned"); // For c++11 and later return n & (n - 1); } Explanation if...

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.

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The <cfparam> tag creates a variable if it does not already exist. You can assign a default value using the default attribute. This can be used if you want to create a variable, but don't want to overwrite it if it has been previously created elsewhere. Here the variable hasn't been set previ...

You can check if a variable has been defined in a scope by using ColdFusion's built in StructKeyExists() function. This can be used inside a <cfif> tag to prevent error messages in the event you attempt to refer to a variable that does not exist. You can also use this function to determine whe...

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}...

We can draw a connection between the Haskell types and the natural numbers. This connection can be made assigning to every type the number of inhabitants it has. Finite union types For finite types, it suffices to see that we can assign a natural type to every number, based in the number of constr...

Lists Lists can be defined as: data List a = Nil | Cons a (List a) If we translate this into our type algebra, we get List(a) = 1 + a * List(a) But we can now substitute List(a) again in this expression multiple times, in order to get: List(a) = 1 + a + a*a + a*a*a + a*a*a*a + ... ...

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...

You can, of course, return lists from subs: sub foo { my @list1 = ( 1, 2, 3 ); my @list2 = ( 4, 5 ); return ( @list1, @list2 ); } my @list = foo(); print @list; # 12345 But it is not the recommended way to do that unless you know what you are doing. While th...

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...