prefer using 3 slash for code comments

dart.html.markdown

@@ -3,27 +3,28 @@ language: dart
 filename: learndart.dart
 contributors:
   - ["Joao Pedrosa", "https://github.com/jpedrosa/"]
+  - ["Vince Ramces Oliveros", "https://github.com/ram231"]
 ---
 
 Dart is a newcomer into the realm of programming languages.
 It borrows a lot from other mainstream languages, having as a goal not to deviate too much from
-its JavaScript sibling. Like JavaScript, Dart aims for great browser integration.
+~~its JavaScript sibling. Like JavaScript, Dart aims for great browser integration.~~
 
-Dart's most controversial feature must be its Optional Typing.
+Dart's most controversial feature must be its ~~Optional Typing~~ Static Type safety and [Sound Type checks](https://dart.dev/guides/language/sound-dart).
 
 ```dart
 import "dart:collection";
-import "dart:math" as DM;
+import "dart:math" as math;
 
-// Welcome to Learn Dart in 15 minutes. http://www.dartlang.org/
+/// Welcome to Learn Dart in 15 minutes. http://dart.dev/
-// This is an executable tutorial. You can run it with Dart or on
+/// This is an executable tutorial. You can run it with Dart or on
-// the Try Dart! site if you copy/paste it there. http://try.dartlang.org/
+/// the Try Dart! site if you copy/paste it there. http://dartpad.dev/
-
+/// You can also run Flutter in DartPad by click the `< > New Pad ` and choose Flutter
-// Function declaration and method declaration look the same. Function
+/// Function declaration and method declaration look the same. Function
-// declarations can be nested. The declaration takes the form of
+/// declarations can be nested. The declaration takes the form of
-// name() {} or name() => singleLineExpression;
+/// name() {} or name() => singleLineExpression;
-// The fat arrow function declaration has an implicit return for the result of
+/// The fat arrow function declaration can be an implicit or explicit return for the result of
-// the expression.
+/// the expression.
 example1() {
   nested1() {
     nested2() => print("Example1 nested 1 nested 2");
@@ -32,29 +33,30 @@ example1() {
   nested1();
 }
 
-// Anonymous functions don't include a name.
+/// Anonymous functions don't include a name.
 example2() {
-  nested1(fn) {
+  //// Explicit return type.
+  nested1(Function<void> fn) {
     fn();
   }
   nested1(() => print("Example2 nested 1"));
 }
 
-// When a function parameter is declared, the declaration can include the
+/// When a function parameter is declared, the declaration can include the
-// number of parameters the function takes by specifying the names of the
+/// number of parameters the function takes by specifying the names of the
-// parameters it takes.
+/// parameters it takes.
 example3() {
   planA(fn(informSomething)) {
     fn("Example3 plan A");
   }
-  planB(fn) { // Or don't declare number of parameters.
+  planB(fn) { /// Or don't declare number of parameters.
     fn("Example3 plan B");
   }
   planA((s) => print(s));
   planB((s) => print(s));
 }
 
-// Functions have closure access to outer variables.
+/// Functions have closure access to outer variables.
 var example4Something = "Example4 nested 1";
 example4() {
   nested1(fn(informSomething)) {
@@ -63,8 +65,8 @@ example4() {
   nested1((s) => print(s));
 }
 
-// Class declaration with a sayIt method, which also has closure access
+/// Class declaration with a sayIt method, which also has closure access
-// to the outer variable as though it were a function as seen before.
+/// to the outer variable as though it were a function as seen before.
 var example5method = "Example5 sayIt";
 class Example5Class {
   sayIt() {
@@ -72,14 +74,14 @@ class Example5Class {
   }
 }
 example5() {
-  // Create an anonymous instance of the Example5Class and call the sayIt
+  /// Create an anonymous instance of the Example5Class and call the sayIt
-  // method on it.
+  /// method on it.
   new Example5Class().sayIt();
 }
 
-// Class declaration takes the form of class name { [classBody] }.
+/// Class declaration takes the form of class name { [classBody] }.
-// Where classBody can include instance methods and variables, but also
+/// Where classBody can include instance methods and variables, but also
-// class methods and variables.
+/// class methods and variables.
 class Example6Class {
   var instanceVariable = "Example6 instance variable";
   sayIt() {
@@ -90,7 +92,7 @@ example6() {
   new Example6Class().sayIt();
 }
 
-// Class methods and variables are declared with "static" terms.
+/// Class methods and variables are declared with "static" terms.
 class Example7Class {
   static var classVariable = "Example7 class variable";
   static sayItFromClass() {
@@ -105,11 +107,11 @@ example7() {
   new Example7Class().sayItFromInstance();
 }
 
-// Literals are great, but there's a restriction for what literals can be
+/// Literals are great, but there's a restriction for what literals can be
-// outside of function/method bodies. Literals on the outer scope of class
+/// outside of function/method bodies. Literals on the outer scope of class
-// or outside of class have to be constant. Strings and numbers are constant
+/// or outside of class have to be constant. Strings and numbers are constant
-// by default. But arrays and maps are not. They can be made constant by
+/// by default. But arrays and maps are not. They can be made constant by
-// declaring them "const".
+/// declaring them "const".
 var example8Array = const ["Example8 const array"],
   example8Map = const {"someKey": "Example8 const map"};
 example8() {
@@ -117,9 +119,9 @@ example8() {
   print(example8Map["someKey"]);
 }
 
-// Loops in Dart take the form of standard for () {} or while () {} loops,
+/// Loops in Dart take the form of standard for () {} or while () {} loops,
-// slightly more modern for (.. in ..) {}, or functional callbacks with many
+/// slightly more modern for (.. in ..) {}, or functional callbacks with many
-// supported features, starting with forEach.
+/// supported features, starting with forEach.
 var example9Array = const ["a", "b"];
 example9() {
   for (var i = 0; i < example9Array.length; i++) {
@@ -136,7 +138,7 @@ example9() {
   example9Array.forEach((e) => print("Example9 forEach loop '${e}'"));
 }
 
-// To loop over the characters of a string or to extract a substring.
+/// To loop over the characters of a string or to extract a substring.
 var example10String = "ab";
 example10() {
   for (var i = 0; i < example10String.length; i++) {
@@ -147,14 +149,14 @@ example10() {
   }
 }
 
-// Int and double are the two supported number formats.
+/// Int and double are the two supported number formats.
 example11() {
   var i = 1 + 320, d = 3.2 + 0.01;
   print("Example11 int ${i}");
   print("Example11 double ${d}");
 }
 
-// DateTime provides date/time arithmetic.
+/// DateTime provides date/time arithmetic.
 example12() {
   var now = new DateTime.now();
   print("Example12 now '${now}'");
@@ -162,7 +164,7 @@ example12() {
   print("Example12 tomorrow '${now}'");
 }
 
-// Regular expressions are supported.
+/// Regular expressions are supported.
 example13() {
   var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$");
   match(s) {
@@ -176,7 +178,7 @@ example13() {
   match(s2);
 }
 
-// Boolean expressions support implicit conversions and dynamic type
+/// Boolean expressions support implicit conversions and dynamic type
 example14() {
   var a = true;
   if (a) {
@@ -186,11 +188,11 @@ example14() {
   if (a) {
     print("true, a is $a");
   } else {
-    print("false, a is $a"); // runs here
+    print("false, a is $a"); /// runs here
   }
 
-  // dynamic typed null can be convert to bool
+  /// dynamic typed null can be convert to bool
-  var b;// b is dynamic type
+  var b;/// b is dynamic type
   b = "abc";
   try {
     if (b) {
@@ -199,35 +201,35 @@ example14() {
       print("false, b is $b");
     }
   } catch (e) {
-    print("error, b is $b"); // this could be run but got error
+    print("error, b is $b"); /// this could be run but got error
   }
   b = null;
   if (b) {
     print("true, b is $b");
   } else {
-    print("false, b is $b"); // runs here
+    print("false, b is $b"); /// runs here
   }
 
-  // statically typed null can not be convert to bool
+  /// statically typed null can not be convert to bool
   var c = "abc";
   c = null;
-  // complie failed
+  /// complie failed
-  // if (c) {
+  /// if (c) {
-  //   print("true, c is $c");
+  ///   print("true, c is $c");
-  // } else {
+  /// } else {
-  //   print("false, c is $c");
+  ///   print("false, c is $c");
-  // }
+  /// }
 }
 
-// try/catch/finally and throw are used for exception handling.
+/// try/catch/finally and throw are used for exception handling.
-// throw takes any object as parameter;
+/// throw takes any object as parameter;
 example15() {
   try {
     try {
       throw "Some unexpected error.";
     } catch (e) {
       print("Example15 an exception: '${e}'");
-      throw e; // Re-throw
+      throw e; /// Re-throw
     }
   } catch (e) {
     print("Example15 catch exception being re-thrown: '${e}'");
@@ -236,8 +238,8 @@ example15() {
   }
 }
 
-// To be efficient when creating a long string dynamically, use
+/// To be efficient when creating a long string dynamically, use
-// StringBuffer. Or you could join a string array.
+/// StringBuffer. Or you could join a string array.
 example16() {
   var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e;
   for (e in a) { sb.write(e); }
@@ -246,8 +248,8 @@ example16() {
   print("Example16 join string array '${a.join()}'");
 }
 
-// Strings can be concatenated by just having string literals next to
+/// Strings can be concatenated by just having string literals next to
-// one another with no further operator needed.
+/// one another with no further operator needed.
 example17() {
   print("Example17 "
       "concatenate "
@@ -255,44 +257,44 @@ example17() {
       "just like that");
 }
 
-// Strings have single-quote or double-quote for delimiters with no
+/// Strings have single-quote or double-quote for delimiters with no
-// actual difference between the two. The given flexibility can be good
+/// actual difference between the two. The given flexibility can be good
-// to avoid the need to escape content that matches the delimiter being
+/// to avoid the need to escape content that matches the delimiter being
-// used. For example, double-quotes of HTML attributes if the string
+/// used. For example, double-quotes of HTML attributes if the string
-// contains HTML content.
+/// contains HTML content.
 example18() {
   print('Example18 <a href="etc">'
       "Don't can't I'm Etc"
       '</a>');
 }
 
-// Strings with triple single-quotes or triple double-quotes span
+/// Strings with triple single-quotes or triple double-quotes span
-// multiple lines and include line delimiters.
+/// multiple lines and include line delimiters.
 example19() {
   print('''Example19 <a href="etc">
 Example19 Don't can't I'm Etc
 Example19 </a>''');
 }
 
-// Strings have the nice interpolation feature with the $ character.
+/// Strings have the nice interpolation feature with the $ character.
-// With $ { [expression] }, the return of the expression is interpolated.
+/// With $ { [expression] }, the return of the expression is interpolated.
-// $ followed by a variable name interpolates the content of that variable.
+/// $ followed by a variable name interpolates the content of that variable.
-// $ can be escaped like so \$ to just add it to the string instead.
+/// $ can be escaped like so \$ to just add it to the string instead.
 example20() {
   var s1 = "'\${s}'", s2 = "'\$s'";
   print("Example20 \$ interpolation ${s1} or $s2 works.");
 }
 
-// Optional types allow for the annotation of APIs and come to the aid of
+/// Optional types allow for the annotation of APIs and come to the aid of
-// IDEs so the IDEs can better refactor, auto-complete and check for
+/// IDEs so the IDEs can better refactor, auto-complete and check for
-// errors. So far we haven't declared any types and the programs have
+/// errors. So far we haven't declared any types and the programs have
-// worked just fine. In fact, types are disregarded during runtime.
+/// worked just fine. In fact, types are disregarded during runtime.
-// Types can even be wrong and the program will still be given the
+/// Types can even be wrong and the program will still be given the
-// benefit of the doubt and be run as though the types didn't matter.
+/// benefit of the doubt and be run as though the types didn't matter.
-// There's a runtime parameter that checks for type errors which is
+/// There's a runtime parameter that checks for type errors which is
-// the checked mode, which is said to be useful during development time,
+/// the checked mode, which is said to be useful during development time,
-// but which is also slower because of the extra checking and is thus
+/// but which is also slower because of the extra checking and is thus
-// avoided during deployment runtime.
+/// avoided during deployment runtime.
 class Example21 {
   List<String> _names;
   Example21() {
@@ -315,7 +317,7 @@ void example21() {
   print("Example21 names '${o.names}' and length '${o.length}'");
 }
 
-// Class inheritance takes the form of class name extends AnotherClassName {}.
+/// Class inheritance takes the form of class name extends AnotherClassName {}.
 class Example22A {
   var _name = "Some Name!";
   get name => _name;
@@ -326,13 +328,13 @@ example22() {
   print("Example22 class inheritance '${o.name}'");
 }
 
-// Class mixin is also available, and takes the form of
+/// Class mixin is also available, and takes the form of
-// class name extends SomeClass with AnotherClassName {}.
+/// class name extends SomeClass with AnotherClassName {}.
-// It's necessary to extend some class to be able to mixin another one.
+/// It's necessary to extend some class to be able to mixin another one.
-// The template class of mixin cannot at the moment have a constructor.
+/// The template class of mixin cannot at the moment have a constructor.
-// Mixin is mostly used to share methods with distant classes, so the
+/// Mixin is mostly used to share methods with distant classes, so the
-// single inheritance doesn't get in the way of reusable code.
+/// single inheritance doesn't get in the way of reusable code.
-// Mixins follow the "with" statement during the class declaration.
+/// Mixins follow the "with" statement during the class declaration.
 class Example23A {}
 class Example23Utils {
   addTwo(n1, n2) {
@@ -351,10 +353,10 @@ example23() {
   print("Example23 addTwo(1, 2) results in '${r2}'");
 }
 
-// The Class constructor method uses the same name of the class and
+/// The Class constructor method uses the same name of the class and
-// takes the form of SomeClass() : super() {}, where the ": super()"
+/// takes the form of SomeClass() : super() {}, where the ": super()"
-// part is optional and it's used to delegate constant parameters to the
+/// part is optional and it's used to delegate constant parameters to the
-// super-parent's constructor.
+/// super-parent's constructor.
 class Example24A {
   var _value;
   Example24A({value: "someValue"}) {
@@ -372,9 +374,9 @@ example24() {
   print("Example24 calling super during constructor '${o2.value}'");
 }
 
-// There's a shortcut to set constructor parameters in case of simpler classes.
+/// There's a shortcut to set constructor parameters in case of simpler classes.
-// Just use the this.parameterName prefix and it will set the parameter on
+/// Just use the this.parameterName prefix and it will set the parameter on
-// an instance variable of same name.
+/// an instance variable of same name.
 class Example25 {
   var value, anotherValue;
   Example25({this.value, this.anotherValue});
@@ -385,9 +387,9 @@ example25() {
     "'${o.anotherValue}'");
 }
 
-// Named parameters are available when declared between {}.
+/// Named parameters are available when declared between {}.
-// Parameter order can be optional when declared between {}.
+/// Parameter order can be optional when declared between {}.
-// Parameters can be made optional when declared between [].
+/// Parameters can be made optional when declared between [].
 example26() {
   var _name, _surname, _email;
   setConfig1({name, surname}) {
@@ -407,13 +409,13 @@ example26() {
   "email '${_email}'");
 }
 
-// Variables declared with final can only be set once.
+/// Variables declared with final can only be set once.
-// In case of classes, final instance variables can be set via constant
+/// In case of classes, final instance variables can be set via constant
-// constructor parameter.
+/// constructor parameter.
 class Example27 {
   final color1, color2;
-  // A little flexibility to set final instance variables with syntax
+  /// A little flexibility to set final instance variables with syntax
-  // that follows the :
+  /// that follows the :
   Example27({this.color1, color2}) : color2 = color2;
 }
 example27() {
@@ -422,11 +424,11 @@ example27() {
   print("Example27 color is '${o.color1}' and '${o.color2}'");
 }
 
-// To import a library, use import "libraryPath" or if it's a core library,
+/// To import a library, use import "libraryPath" or if it's a core library,
-// import "dart:libraryName". There's also the "pub" package management with
+/// import "dart:libraryName". There's also the "pub" package management with
-// its own convention of import "package:packageName".
+/// its own convention of import "package:packageName".
-// See import "dart:collection"; at the top. Imports must come before
+/// See import "dart:collection"; at the top. Imports must come before
-// other code declarations. IterableBase comes from dart:collection.
+/// other code declarations. IterableBase comes from dart:collection.
 class Example28 extends IterableBase {
   var names;
   Example28() {
@@ -439,11 +441,11 @@ example28() {
   o.forEach((name) => print("Example28 '${name}'"));
 }
 
-// For control flow we have:
+/// For control flow we have:
-// * standard switch with must break statements
+/// * standard switch with must break statements
-// * if-else if-else and ternary ..?..:.. operator
+/// * if-else if-else and ternary ..?..:.. operator
-// * closures and anonymous functions
+/// * closures and anonymous functions
-// * break, continue and return statements
+/// * break, continue and return statements
 example29() {
   var v = true ? 30 : 60;
   switch (v) {
@@ -470,17 +472,17 @@ example29() {
     } else {
       continue;
     }
-    // Never gets here.
+    /// Never gets here.
   }
 }
 
-// Parse int, convert double to int, or just keep int when dividing numbers
+/// Parse int, convert double to int, or just keep int when dividing numbers
-// by using the ~/ operation. Let's play a guess game too.
+/// by using the ~/ operation. Let's play a guess game too.
 example30() {
   var gn, tooHigh = false,
     n, n2 = (2.0).toInt(), top = int.parse("123") ~/ n2, bottom = 0;
   top = top ~/ 6;
-  gn = new DM.Random().nextInt(top + 1); // +1 because nextInt top is exclusive
+  gn = new DM.Random().nextInt(top + 1); /// +1 because nextInt top is exclusive
   print("Example30 Guess a number between 0 and ${top}");
   guessNumber(i) {
     if (n == gn) {
@@ -503,8 +505,8 @@ example30() {
   }
 }
 
-// Optional Positional Parameter:
+/// Optional Positional Parameter:
-// parameter will be disclosed with square bracket [ ] & square bracketed parameter are optional.
+/// parameter will be disclosed with square bracket [ ] & square bracketed parameter are optional.
 example31() {
     findVolume31(int length, int breath, [int height]) {
       print('length = $length, breath = $breath, height = $height');
@@ -514,12 +516,12 @@ example31() {
     findVolume31(10,20); //also valid
 }
 
-// Optional Named Parameter:
+/// Optional Named Parameter:
-// parameter will be disclosed with curly bracket { }
+/// parameter will be disclosed with curly bracket { }
-// curly bracketed parameter are optional.
+/// curly bracketed parameter are optional.
-// have to use parameter name to assign a value which separated with colan :
+/// have to use parameter name to assign a value which separated with colan :
-// in curly bracketed parameter order does not matter
+/// in curly bracketed parameter order does not matter
-// these type parameter help us to avoid confusion while passing value for a function which has many parameter.
+/// these type parameter help us to avoid confusion while passing value for a function which has many parameter.
 example32() {
     findVolume32(int length, int breath, {int height}) {
     print('length = $length, breath = $breath, height = $height');
@@ -529,9 +531,9 @@ example32() {
     findVolume32(10,20);//also valid
 }
 
-// Optional Default Parameter:
+/// Optional Default Parameter:
-// same like optional named parameter in addition we can assign default value for this parameter.
+/// same like optional named parameter in addition we can assign default value for this parameter.
-// which means no value is passed this default value will be taken.
+/// which means no value is passed this default value will be taken.
 example33() {
     findVolume33(int length, int breath, {int height=10}) {
      print('length = $length, breath = $breath, height = $height');
@@ -541,11 +543,11 @@ example33() {
     findVolume33(10,20);//valid
 }
 
-// Programs have only one entry point in the main function.
+/// Programs have only one entry point in the main function.
-// Nothing is expected to be executed on the outer scope before a program
+/// Nothing is expected to be executed on the outer scope before a program
-// starts running with what's in its main function.
+/// starts running with what's in its main function.
-// This helps with faster loading and even lazily loading of just what
+/// This helps with faster loading and even lazily loading of just what
-// the program needs to startup with.
+/// the program needs to startup with.
 main() {
   print("Learn Dart in 15 minutes!");
   [example1, example2, example3, example4, example5, example6, example7,
@@ -564,6 +566,3 @@ Dart has a comprehensive web-site. It covers API reference, tutorials, articles
 useful Try Dart online.
 [https://www.dartlang.org](https://www.dartlang.org)
 [https://try.dartlang.org](https://try.dartlang.org)
-
-
-