Tutorial by Examples: u

Bitwise XOR (Exclusive OR)

The ^ operator will perform a binary XOR in which a binary 1 is copied if and only if it is the value of exactly one operand. Another way of stating this is that the result is 1 only if the operands are different. Examples include: # 0 ^ 0 = 0 # 0 ^ 1 = 1 # 1 ^ 0 = 1 # 1 ^ 1 = 0 # 60 = 0b1111...

Python Language • Bitwise Operators

Numerical comparisons

Numerical comparisons use the -eq operators and friends if [[ $num1 -eq $num2 ]]; then echo "$num1 == $num2" fi if [[ $num1 -le $num2 ]]; then echo "$num1 <= $num2" fi There are six numeric operators: -eq equal -ne not equal -le less or equal -lt less than ...

Bash • Conditional Expressions

Functions with arguments

In helloJohn.sh: #!/bin/bash greet() { local name="$1" echo "Hello, $name" } greet "John Doe" # running above script $ bash helloJohn.sh Hello, John Doe If you don't modify the argument in any way, there is no need to copy it to a local variabl...

Bash • Functions

Background Gradients

Gradients are new image types, added in CSS3. As an image, gradients are set with the background-image property, or the background shorthand. There are two types of gradient functions, linear and radial. Each type has a non-repeating variant and a repeating variant: linear-gradient() repeating-...

CSS • Backgrounds

Named Capture Groups

Some regular expression flavors allow named capture groups. Instead of by a numerical index you can refer to these groups by name in subsequent code, i.e. in backreferences, in the replace pattern as well as in the following lines of the program. Numerical indexes change as the number or arrangemen...

Regular Expressions • Capture Groups

Zero value of a map

The zero value of a map is nil and has a length of 0. var m map[string]string fmt.Println(m == nil) // true fmt.Println(len(m) ==0) // true A nil map has no keys nor can keys be added. A nil map behaves like an empty map if read from but causes a runtime panic if written to. var m map[string]...

Go • Maps

Waiting for goroutines

Go programs end when the main function ends, therefore it is common practice to wait for all goroutines to finish. A common solution for this is to use a sync.WaitGroup object. package main import ( "fmt" "sync" ) var wg sync.WaitGroup // 1 func routine(i int...

Go • Concurrency

Logging Variable Values

You shouldn't call NSLog without a literal format string like this: NSLog(variable); // Dangerous code! If the variable is not an NSString, the program will crash, because NSLog expects an NSString. If the variable is an NSString, it will work unless your string contains a %. NSLog will pars...

Objective-C Language • Logging

Using ThreadLocal

A useful tool in Java Concurrency is ThreadLocal – this allows you to have a variable that will be unique to a given thread. Thus, if the same code runs in different threads, these executions will not share the value, but instead each thread has its own variable that is local to the thread. For exa...

Java Language • Concurrent Programming (Threads)

Finding out the Number of Elements in an Array

NSArray *myColors = [NSArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; NSLog (@"Number of elements in array = %lu", [myColors count]);

Objective-C Language • NSArray

Spanning columns or rows

Table cells can span multiple columns or rows using the colspan and rowspan attributes. These attributes can be applied to <th> and <td> elements. <table> <tr> <td>row 1 col 1</td> <td>row 1 col 2</td> <td>row 1 c...

HTML • Tables

Element Language

The lang attribute is used to specify the language of element content and attribute text values: The content of this element is in English. The content of this el...

HTML • Content Languages

Elements with Multiple Languages

You can "overwrite" a language declaration: This English sentence contains the German word Hallo.

HTML • Content Languages

Handling Attributes with Different Languages

You can "overwrite" a parent element's language declaration by introducing any element apart from applet, base, basefont, br, frame, frameset, hr, iframe, meta, param, script (of HTML 4.0) with an own lang attribute: ...

HTML • Content Languages

Base Document Language

It’s a good practice to declare the primary language of the document in the html element: <html lang="en"> If no other lang attribute is specified in the document, it means that everything (i.e., element content and attribute text values) is in that language. If the document con...

HTML • Content Languages

Fixtures

From Wikipedia: A test fixture is something used to consistently test some item, device, or piece of software. It can also enhance readability of tests by extracting common initialisation / finalisation code from the test methods themselves. Where common initialisation can be executed once in...

junit • Tests

Simple usage

Object initializers are handy when you need to create an object and set a couple of properties right away, but the available constructors are not sufficient. Say you have a class public class Book { public string Title { get; set; } public string Author { get; set; } // the rest o...

C# Language • Object initializers

Usage with anonymous types

Object initializers are the only way to initialize anonymous types, which are types generated by the compiler. var album = new { Band = "Beatles", Title = "Abbey Road" }; For that reason object initializers are widely used in LINQ select queries, since they provide a convenie...

C# Language • Object initializers

Recurse the whole pattern

The construct (?R) is equivalent to (?0) (or \g<0>) - it lets you recurse the whole pattern: <(?>[^<>]+|(?R))+> This will match properly balanced angle brackets with any text in-between the brackets, like <ac<d>e>.

Regular Expressions • Recursion

Recurse into a subpattern

You can recurse into a subpattern using the following constructs (depending on the flavor), assuming n is a capturing group number, and name the name of a capturing group. (?n) \g<n> \g'0' (?&name) \g<name> \g'name' (?P>name) The following pattern: \[(?<angle>&...

Regular Expressions • Recursion