rmnblm

using System;
using System.Windows.Input;

/// <summary>
/// A command whose sole purpose is to relay its functionality to 
/// other objects by invoking delegates. 
/// The default return value for the CanExecute method is 'true'.
/// </summary>
public class RelayCommand : ICommand
{

rmnblm

// Declare three optional variables
var firstName: String?
var lastName: String?
var age: Int?

// EXAMPLE: if-Statement
if let firstName = firstName {
    if let lastName = lastName {
        if let age = age, age >= 18 {
            doSomething(firstName, lastName, age)

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// Declare an optional value
var name: String? = "Roman"

// Optional chaining
name?.characters.count

if name != nil {
  // Force unwrap
  name!.characters.count
}

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// Declare two optional values
var firstName: String? = "Roman"
var lastName: String? = "Blum"

// Option 1: Nested
if let firstName = firstName {
  if let lastName = lastName {
    // Use firstName and lastName
  }
}

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/* Example JSON Object

  {
    "key": {
      "nestedKey": {
        "nestedKey": {
          "nestedKey": 42.0
        }
      }
    }

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// Declare an optional variable
var name: String? = "Roman"

guard let name = name else {
  print("name is nil")
  return
}

print(name) 
// Output: Roman

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var text: String?
print(text)
// Output: nil
print(text ?? "B")
// Output: B
text = "A"
print(text ?? "B")
// Output: A
print(text)
// Output: Optional("A")

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OS X Screencast to animated GIF

This gist shows how to create a GIF screencast using only free OS X tools: QuickTime, ffmpeg, and gifsicle.

Instructions

To capture the video (filesize: 19MB), using the free "QuickTime Player" application:

rmnblm

// int num = null; -> Error
int? num = null;

if (num.HasValue)
{
    System.Console.WriteLine("num = " + num.Value);
}
else
{
    System.Console.WriteLine("num = Null");

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(function () {
  l1 = 'STEP 1';
  console.log(l1);          // Output: STEP 1

  if (true) {
    console.log(l1);        // Output: STEP 1
    var l1 = 'STEP 2';      // var isn't block-scoped, gets hoisted
    console.log(l1);        // Output: STEP 2
  }