Dart Basics

DartBasics.dart

/* 
 * Dart Basics: 
 * Written By: Kyra Samuel
 * Coded By: Kyra Samuel 
 * Twitter/GitHub/Discord: @modernlabrat
 * Sources: 
 * * * * * * Udemy - Flutter & Dart - The Completed Guide [2020 Edition]
 * * * * * * O'Reilly - Programming Flutter
 * 
 * Dart is an object-oriented programming language.
 * Dart is camel-case, like Java
 * Dart is strong-typed. 
 * 
 * Add type, or it will assume a dynamic type (accepts any value) Avoid!!
 * Assign implicit types.
 * 
 * Follows the semi-colon ruling like Java.
 * 
 * Basic Data Types: String, int, double, num type allows both
 * integer and doubles 
 * 
 * Comments: Single/Multi-Line
 * 
 * Backlash - escape characters, enclosed string quotes, \\ escaped
 * backlash.
 * 
*/

/*
 * void functions return nothing. 
 * You cannot print void functionName() as it doesn't return anything. 
 * Single line functions do not use semi-colons. 
 * Use => for one line of code in the function body.
 * 
*/

int addNumbers(int num1, int num2) => num1 + num2; // A function or method that adds two integers, num1 and num2, passed into the parameters.
  

/*
 * Create a class to define the blueprint of an object. 
 * Naming Convention for classes == Uppercase
 */

class Person {
  /* variables in classes are sometimes called 'properties'
   * variables in functions are called 'variables'
   * immutable variables: final and const, replaces keyword var
   * * * * can be prefixed like so - final String name = 'Kyra';
   * final: needed for all widget properties in Flutter, widgets are
   * immutable.
   * const: used to create compile-time constants. no const arguments.
   */
  
  String name; // decalred with String because there is not an initial value.
  
  /* Strings can be single or double quotes.
   * The operator plus is used to concatenate / interpolate strings.
   * String properties: codeUnits, isEmpty, Length
   * Some String methods: toLowerCase(), toUpperCase(), trim(),
   * compareTo(), replaceAll(), split(), subString()
  */
  int age; // since there is not initial value, use 'int' instead of 'var'
  
  void greet() { // greet() function prints a personal greeting for a Person object.
    print('Hi, I am ' + name + ' and I am ' + age.toString()); // use toString() for int, double, and float values.
  }
}

void main() { // Dart Starts Here First!!
  
  // use print() like Python or console.log() like Javascript
  print(addNumbers(4,2)); // I am passing 3 and 4 to addNumbers() and calling the function.
 
  
  /* 
   * Dart has 'type inference'
   * 
   * To declare variables use the keyword 'var'
   * To declare constant variables use the keyword 'final'
   * Declare variables with an implicit type if there is not an inital
   * value assigned.
   * 
  */
  
  var nine = addNumbers(4, 5); // Store result of addNumbers(4,5) into an integer variable named nine
  print(nine);
  
  var ten = addNumbers(3,7);
 
  var nineteen = nine + ten; // adding variables together
  print(nineteen);
  
  int two = addNumbers(1,1);
  int three = addNumbers(1, two);
  print(three);
  
  // Creating an instance of the Person class.
  
  var person1 = Person(); // Dart doesn't require the new keyword, although it can be used.
  
  person1.age = 32; // Assigning values to person1 i.e age, name
  person1.name = 'Kyra';
  
  print('person1: ${person1.age}'); // ${} can be used to interpolate a value in a Dart expression.
  
  print(person1.name);
  person1.greet(); // Calling the greet function on the Person person1 instance.
  
   /* 
    * assert() is for testing/debugging - terminates the code if the
    * condition is FALSE. Assume the condition is true in the parenthesis.
    *  
    */
  
  assert(two =='2');
  
  // Lists
  
  /*
   * Lists are an ordered collection of data
   * Elements are indexed from 0 to length-1
   * Lists can have If and For loops nested inside.
   * Lists can be created by the List.generate constructor, which takes two
   * arguments: the numbers of elements and a callback function that
   * generates each element based on its index.
   * 
   * A callback function: a function to be run by another function in
   * certain conditions and with certain arguments.
   * 
  */
    
  var condition = two == 2;
  var list1 = [
    if(condition) print('two') // notice the lack of semicolons 
    else print('not two')
  ];
  
  print(list1);
  
  var list2 = [20,30,40]; // create a list
  assert(list2[0] == 20); // get a list value by splicing the list with square brackets and the appropiate index value.
  print(list2);
  
  // add/remove items to/from a list
  list2.add(50);
  print(list2);
  
  list2.remove(20);
  print(list2);
  
  list2.removeAt(1); // removing an element by its index.
  print(list2);
  
  var list3 = [60, 70];
  
  // iterate over lists: for, map, forEach
  
  for(var number in list2) {  // for
    print(number);
  }
  
  /*
   * map and forEach are alternativs to the for in loop
   * forEach similar to for with a callback type of void
   * 
  */
  
  list2.forEach((number) {
    print(number);
  }); // note the syntax forEach()
  
  /* 
   * .map creates an Iterable. Below the variable 'iter' is an Iterable,
   *  not a List, so use the toList method for appropiate List conversion.
   * 
  */
  
  var iter = list2.map((number) => "#$number").toList(); // Note the added # symbol in the output.
  print(iter);
  
  /*
   * Ternary operators are used to
   * evaluate a single line
   * condition.
   * 
   */
  
  var condition2 = true; // execute a statement
  condition2 ? print('when i\'m true') : print( 'when i\'m false');
  
}