Tutorial by Examples: v

Diagnosing a problem with a service

On systems using systemd, such as Fedora => 15, Ubuntu (Server and Desktop) >= 15.04, and RHEL/CentOS >= 7: systemctl status [servicename] ...where [servicename] is the service in question; for example, systemctl status sshd. This will show basic status information and any recent errors ...

GNU/Linux • Managing Services

Mixin with variable argument

There are some cases in mixins where there can be single or multiple arguments while using it. Let's take a case of border-radius where there can be single argument like border-radius:4px; or multiple arguments like border-radius:4px 3px 2px 1px;. Traditional with Keyword Arguments mixing will be l...

sass • Mixins

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

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

Copy, move or delete found line

A lot of users find themselves in a situation where they just want to copy, move or delete a line quickly and return to where they were. Usually, if you'd want to move a line which contains the word lot below the current line you'd type something like: /lot<Esc>dd<C-o>p But to boost...

vim • Tips and tricks to boost productivity

When to use a Static variable

A Static variable declared locally is not destructed and does not lose its value when the Sub procedure is exited. Subsequent calls to the procedure do not require re-initialization or assignment although you may want to 'zero' any remembered value(s). These are particularly useful when late bindin...

VBA • Declaring Variables

Infinite Streams via Recursion

Streams can be built that reference themselves and thus become infinitely recursive. // factorial val fact: Stream[BigInt] = 1 #:: fact.zipWithIndex.map{case (p,x)=>p*(x+1)} fact.take(10) // (1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880) fact(24) // 620448401733239439360000 // the ...

Scala Language • Streams

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

Animate an image across the Canvas

This example loads and animates and image across the Canvas Important Hint! Make sure you give your image time to fully load by using image.onload. Annotated Code <!doctype html> <html> <head> <style> body{ background-color:white; } #canvas{border:1px solid re...

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

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

Recover

Recover as the name implies, can attempt to recover from a panic. The recover must be attempted in a deferred statement as normal execution flow has been halted. The recover statement must appear directly within the deferred function enclosure. Recover statements in functions called by deferred f...

Go • Panic and Recover

Tutorial by Examples: v

Diagnosing a problem with a service

Mixin with variable argument

DecimalPropertyConvention

Using the revert command to discard unwanted changes.

Primitive to Primitive conversion table

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

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

Copy, move or delete found line

When to use a Static variable

Infinite Streams via Recursion

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

Use requestAnimationFrame() NOT setInterval() for animation loops

Animate an image across the Canvas

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

Working with Varargs parameters

Even and Odd Numbers

Recover

Default value of nullable types is null

Right shift of a negative integer

Assigning an out-of-range value to an integer