Tutorial by Examples: anti

You should not save props into state. It is considered an anti-pattern. For example: export default class MyComponent extends React.Component { constructor() { super(); this.state = { url: '' } this.onChange = this.onChange.bind(this); ...

class Lion { private double weight; // only accessible with-in class this(double weight) { this.weight = weight; } double weightInPounds() const @property // const guarantees no modifications // @property functions are treated as fields { ret...

A Semantic Model offers a deeper level of interpretation and insight of code compare to a syntax tree. Where syntax trees can tell the names of variables, semantic models also give the type and all references. Syntax trees notice method calls, but semantic models give references to the precise locat...

The value of a type hole can simply said to be undefined, although a typed hole triggers a compile-time error, so it is not strictly necessary to assign it a value. However, a typed hole (when they are enabled) produces a compile time error (or warning with deferred type errors) which states the nam...

If you have a greedy match as the first quantifier, the whole RE will be greedy, If you have non-greedy match as the first quantifier, the whole RE will be non-greedy. set mydata { Device widget1: port: 156 alias: input2 Device widget2: alias: input1 Device widget3: port: 238 alias...

The std::nth_element algorithm takes three iterators: an iterator to the beginning, nth position, and end. Once the function returns, the nth element (by order) will be the nth smallest element. (The function has more elaborate overloads, e.g., some taking comparison functors; see the above link for...

This basic example shows how an application can instantiate a classloader and use it to dynamically load a class. URL[] urls = new URL[] {new URL("file:/home/me/extras.jar")}; Classloader loader = new URLClassLoader(urls); Class<?> myObjectClass = loader.findClass("com.exampl...

Possessive quantifiers are another class of quantifiers in many regex flavours that allow backtracking to, effectively, be disabled for a given token. This can help improve performance, as well as preventing matches in certain cases. The class of possessive quantifiers can be distinguished from laz...

This example deals with one of the most fundamental aspects of the VHDL language: the simulation semantics. It is intended for VHDL beginners and presents a simplified view where many details have been omitted (postponed processes, VHDL Procedural Interface, shared variables...) Readers interest...

Using the Swift class Mirror works if you want to extract name, value and type (Swift 3: type(of: value), Swift 2: value.dynamicType) of properties for an instance of a certain class. If you class inherits from NSObject, you can use the method class_copyPropertyList together with property_getAttrib...

We may forget to apply the Antiforgery attribute for each POST request so we should make it by default. This sample will make sure Antiforgery filter will always be applied to every POST request. Firstly create new AntiForgeryTokenFilter filter: //This will add ValidateAntiForgeryToken Attribute t...

First off you create the form @using (Html.BeginForm()) { @Html.AntiForgeryToken() } Action Method [HttpPost] [ValidateAntiForgeryToken] public ActionResult Test(FormViewModel formData) { // ... } Script <script src="https://code.jquery.com/jquery-1.12.4.min.js"&g...

Let's say we have two tables (A and B) and some of their rows match (relative to the given JOIN condition, whatever it may be in the particular case): We can use various join types to include or exclude matching or non-matching rows from either side, and correctly name the join by picking the cor...

Let's say that we're given const string input as a phone number to be validated. We could start by requiring a numeric input with a zero or more quantifier: regex_match(input, regex("\\d*")) or a one or more quantifier: regex_match(input, regex("\\d+")) But both of those really f...

An instantiation error is thrown if an argument is not sufficiently instantiated. Critically, an instantiation error cannot be replaced by silent failure: Failing in such cases would mean that there is no solution, whereas an instantiation error means that an instance of the argument may participat...

From android 6.0 this permission needs to grant dynamically, <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/> Throwing below permission denied error on 6.0, Caused by: android.view.WindowManager$BadTokenException: Unable to add window android.view.ViewRoo...

[![Sample equation][1]][1] sympy provides its solution as a Python set of expressions in terms of parametric variables, as shown here in the final line. >>> from sympy.solvers.diophantine import diophantine >>> from sympy import var >>> x,y,z=var('x y z') >>>...

Avoid this Anti-Pattern var myDeferred = $q.defer(); $http(config).then(function(res) { myDeferred.resolve(res); }, function(error) { myDeferred.reject(error); }); return myDeferred.promise; There is no need to manufacture a promise with $q.defer as the $http service alread...

Locking on an stack-allocated / local variable One of the fallacies while using lock is the usage of local objects as locker in a function. Since these local object instances will differ on each call of the function, lock will not perform as expected. List<string> stringList = new List<st...

An explicit instantiation definition creates and declares a concrete class, function, or variable from a template, without using it just yet. An explicit instantiation can be referenced from other translation units. This can be used to avoid defining a template in a header file, if it will only be i...