Tutorial by Examples: er

The role of placeholders in "enter" selections

What is an enter selection? In D3.js, when one binds data to DOM elements, three situations are possible: The number of elements and the number of data points are the same; There are more elements than data points; There are more data points than elements; In the situation #3, all the data ...

d3.js • Selections

Rounded corners

layer.masksToBounds = true; layer.cornerRadius = 8;

iOS • CALayer

List iteration: foreach

foreach varlist1 list1 ?varlist2 list2 ...? body foreach is a powerful control structure that allows looping over a list or multiple lists. set alpha [list a b c d e f] foreach {key} $alpha { puts "key: $key" } Multiple variable names may be specified. set alphaindexes [list a ...

tcl • Control Structures

Inheritance of Singleton Class

Subclassing also Subclasses Singleton Class class Example end Example.singleton_class #=> #<Class:Example> def Example.foo :example end class SubExample < Example end SubExample.foo #=> :example SubExample.singleton_class.superclass #=> #<Class:Example> ...

Ruby Language • Singleton Class

DecimalPropertyConvention

By default Entity Framework maps decimal properties to decimal(18,2) columns in database tables. public class Box { public int Id { set; get; } public decimal Length { set; get; } public decimal Width { set; get; } public decimal Height { set; get; } } We can change the p...

Entity Framework • Code First Conventions

difference between two commit or branch

To view difference between two branch git diff <branch1>..<branch2> To view difference between two branch git diff <commitId1>..<commitId2> To view diff with current branch git diff <branch/commitId> To view summary of changes git diff --stat <branch/com...

Git • Git Diff

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

Primitive to Primitive conversion table

ValueConverted To StringConverted To NumberConverted To Booleanundefinded"undefined"NaNfalsenull"null"0falsetrue"true"1false"false"0NaN"NaN"false"" empty string0false" "0true"2.4" (numeric)2.4true"test" (non nu...

JavaScript • Variable coercion/conversion

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

Avoiding duplication of code in const and non-const getter methods.

In C++ methods that differs only by const qualifier can be overloaded. Sometimes there may be a need of two versions of getter that return a reference to some member. Let Foo be a class, that has two methods that perform identical operations and returns a reference to an object of type Bar: class ...

C++ • const keyword

List files and folders

To list files and folders inside current directory, we use ls command: user@host:/$ ls bin boot cdrom dev etc home initrd.img lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var vmlinuz ls prints folder structure in simple view, color coded by type....

Ubuntu • Basic Terminal commands

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

Use requestAnimationFrame() NOT setInterval() for animation loops

requestAnimationFrame is similar to setInterval, it but has these important improvements: The animation code is synchronized with display refreshes for efficiency The clear + redraw code is scheduled, but not immediately executed. The browser will execute the clear + redraw code only when the d...

html5-canvas • Animation

Don't draw animations in your event handlers (a simple sketch app)

During mousemove you get flooded with 30 mouse events per second. You might not be able to redraw your drawings at 30 times per second. Even if you can, you're probably wasting computing power by drawing when the browser is not ready to draw (wasted == across display refresh cycles). Therefore it m...

html5-canvas • Animation

Runtime Code Generation

<#@ template language="C#" #> //Language of your project <#@ assembly name="System.Core" #> <#@ import namespace="System.Linq" #> <#@ import namespace="System.Text" #> <#@ import namespace="System.Collections.Generic" ...

C# Language • T4 Code Generation

UIColor from an image pattern

You can create a UIColor object using an image pattern by using the UIColor(patternImage:_) method. btn.backgroundColor = UIColor(patternImage: UIImage(named: "image")!)

iOS • UIColor

Working with Varargs parameters

Using varargs as a parameter for a method definition, it is possible to pass either an array or a sequence of arguments. If a sequence of arguments are passed, they are converted into an array automatically. This example shows both an array and a sequence of arguments being passed into the printVar...

Java Language • Varargs (Variable Argument)

Even and Odd Numbers

The even? method can be used to determine if a number is even 4.even? # => true 5.even? # => false The odd? method can be used to determine if a number is odd 4.odd? # => false 5.odd? # => true

Ruby Language • Numbers

Rounding Numbers

The round method will round a number up if the first digit after its decimal place is 5 or higher and round down if that digit is 4 or lower. This takes in an optional argument for the precision you're looking for. 4.89.round # => 5 4.25.round # => 4 3.141526.round(1) # => ...

Ruby Language • Numbers

Restrict Number to Min/Max Range

If you need to clamp a number to keep it inside a specific range boundary function clamp(min, max, val) { return Math.min(Math.max(min, +val), max); } console.log(clamp(-10, 10, "4.30")); // 4.3 console.log(clamp(-10, 10, -8)); // -8 console.log(clamp(-10, 10, 12)); // ...

JavaScript • Arithmetic (Math)