Tutorial by Examples: ed

Using the revert command to discard unwanted changes.

The revert command allows discarding unwanted uncommitted changes. Reverting changes to a single file. hg revert example.c Reverting all changes. This will discard all changes not just the current directory. hg revert --all hg will output which files were reverted. reverting exa...

mercurial • Common operations

Deleting a derived object via a pointer to a base class that doesn't have a virtual destructor.

class base { }; class derived: public base { }; int main() { base* p = new derived(); delete p; // The is undefined behavior! } In section [expr.delete] §5.3.5/3 the standard says that if delete is called on an object whose static type does not have a virtual destructor: if the...

C++ • Undefined Behavior

Animate at a specified interval (add a new rectangle every 1 second)

This example adds a new rectangle to the canvas every 1 second (== a 1 second interval) Annotated Code: <!doctype html> <html> <head> <style> body{ background-color:white; } #canvas{border:1px solid red; } </style> <script> window.onload=(functio...

html5-canvas • Animation

Animate at a specified time (an animated clock)

This example animates a clock showing the seconds as a filled wedge Annotated Code: <!doctype html> <html> <head> <style> body{ background-color:white; } #canvas{border:1px solid red; } </style> <script> window.onload=(function(){ // canva...

html5-canvas • Animation

Iterating manually through analyzed tokens

TokenStream stream = myAnalyzer.tokenStream("myField", textToAnalyze); stream.addAttribute(CharTermAttribute.class); stream.reset(); while(stream.incrementToken()) { CharTermAttribute token = stream.getAttribute(CharTermAttribute.class); System.out.println(token.toString()); ...

lucene • Analysis

Hello, World! (modular, object-oriented)

import tkinter as tk class HelloWorld(tk.Frame): def __init__(self, parent): super(HelloWorld, self).__init__(parent) self.label = tk.Label(self, text="Hello, World!") self.label.pack(padx=20, pady=20) if __name__ == "__main__": ...

tkinter • Getting started with tkinter

Removing unwanted characters from a string

The example Checking a string for unwanted characters, describes how to test and reject strings that don't meet certain criteria. Obviously, rejecting input outright is not always possible, and sometimes you just have to make do with what you receive. In these cases, a cautious developer will attemp...

guava • Strings

Connecting overloaded signals/slots

While being better in many regards, the new connection syntax in Qt5 has one big weakness: Connecting overloaded signals and slots. In order to let the compiler resolve the overloads we need to use static_casts to member function pointers, or (starting in Qt 5.7) qOverload and friends: #include &lt...

Qt • Signals and Slots

Both methods implemented, eval-round-trip style repr()

class Card: special_names = {1:'Ace', 11:'Jack', 12:'Queen', 13:'King'} def __init__(self, suit, pips): self.suit = suit self.pips = pips # Called when instance is converted to a string via str() # Examples: # print(card1) # print(str(card1) ...

Python Language • String representations of class instances: __str__ and __repr__ methods

Simple Directed and Non-directed Network Graphing

The igraph package for R is a wonderful tool that can be used to model networks, both real and virtual, with simplicity. This example is meant to demonstrate how to create two simple network graphs using the igraph package within R v.3.2.3. Non-Directed Network The network is created with this pie...

R Language • Network analysis with the igraph package

Non-blocking blinky with the elapsedMillis library (and class)

The elapsedMillis library provides a class with the same name that keeps track of the time that passed since it was created or set to a certain value: #include <elapsedMillis.h> #define OUTPIN LED_BUILTIN #define PERIOD 500 elapsedMillis ledTime; bool ledState = false; void setup...

arduino • Time Management

Measure how long something took, using elapsedMillis and elapsedMicros

#include <elapsedMillis.h> void setup() { Serial.begin(115200); elapsedMillis msTimer; elapsedMicros usTimer; long int dt = 500; delay(dt); long int us = usTimer; long int ms = msTimer; Serial.print("delay(");Serial.print(dt);Serial.println(") to...

arduino • Time Management

Prevent a mixin definition from appearing in the compiled CSS file

.default-settings() { padding: 4px; margin: 4px; font-size: 16px; border: 1px solid gray; } #demo { .default-settings; } The above example when compiled would only produce the following output. The .default-settings() mixin definition would not be output in the compiled CSS fi...

less • Mixins

Creating a Sorted Entity System

A simple EntitySystem that processes each entity of a given family in the order specified by a comparator and calls processEntity() for each entity every time the EntitySystem is updated. This is really just a convenience class as rendering systems tend to iterate over a list of entities in a sort...

libgdx • Ashley Entity System

The dict get command can raise an error

set alpha {a 1 b 2 c 3} dict get $alpha b # => 2 dict get $alpha d # (ERROR) key "d" not known in dictionary If dict get is used to retrieve the value of a missing key, an error is raised. To prevent the error, use dict exists: if {[dict exists $alpha $key]} { set result [d...

tcl • Dictionaries

Usage of the SelectedDate property

The DatePicker class has a property, SelectedDate, which enable you to get or set the selected date. If there is none selected, it means its value will be null. if (datePicker.SelectedDate == null) { // Do what you have to do }

datepicker • Check if DatePicker value is null

Retrieve Specified User's Out of Office Settings

First let's create an ExchangeManager object, where the constructor will connect to the services for us. It also has a GetOofSettings method, which will return the OofSettings object for the specified email address : using System; using System.Web.Configuration; using Microsoft.Exchange.WebServic...

C# Language • Microsoft.Exchange.WebServices

Manipulating records that fired the trigger

trigger MyTrigger on SomeObject__c (after insert, after update) { if (Trigger.isAfter && Trigger.isInsert) { System.debug('The following records were inserted: '); for (SomeObject__c o : Trigger.new) { System.debug(o.Name); } } else if (Trigg...

Salesforce • Apex Triggers

Named routes in Django-style

One big problem is that valuable named routes is not supported by Express out of the box. Solution is to install supported third-party package, for example express-reverse: npm install express-reverse Plug it in your project: var app = require('express')(); require('express-reverse')(app); ...

Node.js • Web Apps With Express

Highlighted and Highlighted Text Color

Objective-C UILabel *label = [[UILabel alloc] init]; label.highlighted = YES; label.highlightedTextColor = [UIColor redColor]; Swift let label = UILabel() label.highlighted = true label.highlightedTextColor = UIColor.redColor() Swift 3 let label = UILabel() label.isHighlighted = true ...

iOS • UILabel