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diff --git a/dart.html.markdown b/dart.html.markdown
index 07f755f7..2672dc6a 100644
--- a/dart.html.markdown
+++ b/dart.html.markdown
@@ -2,127 +2,229 @@
language: dart
filename: learndart.dart
contributors:
- - ["Joao Pedrosa", "https://github.com/jpedrosa/"]
+ - ["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.
+**Dart** is a single threaded, general puprose programming languages.
+It borrows a lot from other mainstream languages.
+It supports Streams, Futures(known as Promises in JavaScript), Generics, First-class functions(closures) and static type checking.
+Dart can run in any platform such as Web, CLI, Desktop, Mobile and IoT devices.
-Dart's most controversial feature must be its Optional Typing.
+Dart's most controversial feature is 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;
-
-// Welcome to Learn Dart in 15 minutes. http://www.dartlang.org/
-// 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/
-
-// Function declaration and method declaration look the same. Function
-// declarations can be nested. The declaration takes the form of
-// name() {} or name() => singleLineExpression;
-// The fat arrow function declaration has an implicit return for the result of
-// the expression.
+import "dart:math" as math;
+
+/// Welcome to Learn Dart in 15 minutes. http://dart.dev/
+/// This is an executable tutorial. You can run it with Dart or on
+/// 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
+
+
+/// In Dart, Everything is an Object.
+/// Every declaration of an object is an instance of Null and
+/// Null is also an object.
+
+
+/// 3 Types of comments in dart
+// Single line comment
+/**
+* Multi-line comment
+* Can comment more than 2 lines
+*/
+/// Code doc comment
+/// It uses markdown syntax to generate code docs when making an API.
+/// Code doc comment is the recommended choice when documenting your APIs, classes and methods.
+
+/// 4 types of variable declaration.
+/// Constants are variables that are immutable cannot be change or altered.
+/// `const` in dart should practice SCREAMING_SNAKE_CASE name declaration.
+const CONSTANT_VALUE = "I CANNOT CHANGE";
+CONSTANT_VALUE = "DID I?"; //Error
+/// Final is another variable declaration that cannot be change once it has been instantiated. Commonly used in classes and functions
+/// `final` can be declared in pascalCase.
+final finalValue = "value cannot be change once instantiated";
+finalValue = "Seems not"; //Error
+
+/// `var` is another variable declaration that is mutable and can change its value. Dart will infer types and will not change its data type
+var mutableValue = "Variable string";
+mutableValue = "this is valid";
+mutableValue = false; // Error.
+
+/// `dynamic` is another variable declaration in which the type is not evaluated by the dart static type checking.
+/// It can change its value and data type.
+/// Some dartisans uses dynamic cautiously as it cannot keep track of its data type. so use it at your own risk
+dynamic dynamicValue = "I'm a string";
+dynamicValue = false; // false
+
+
+/// Functions can be declared in a global space
+/// Function declaration and method declaration look the same. Function
+/// declarations can be nested. The declaration takes the form of
+/// name() {} or name() => singleLineExpression;
+/// The fat arrow function declaration can be an implicit or
+/// explicit return for the result of the expression.
+/// Dart will execute a function called `main()` anywhere in the dart project.
+///
example1() {
nested1() {
nested2() => print("Example1 nested 1 nested 2");
nested2();
}
+
nested1();
}
-// Anonymous functions don't include a name.
+/// Anonymous functions don't include a name but can take number of arguments
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
-// number of parameters the function takes by specifying the names of the
-// parameters it takes.
+/// When a function parameter is declared, the declaration can include the
+/// number of parameters the function takes by explicitly specifying the names of the
+/// parameters it takes.
example3() {
- planA(fn(informSomething)) {
+ planA(fn(String 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.
+/// Dart will infer types when the variable has a value of something.
+/// In this example dart knows that this variable is a String.
var example4Something = "Example4 nested 1";
example4() {
nested1(fn(informSomething)) {
fn(example4Something);
}
+
nested1((s) => print(s));
}
-// Class declaration with a sayIt method, which also has closure access
-// to the outer variable as though it were a function as seen before.
+/// Class declaration with a sayIt method, which also has closure access
+/// to the outer variable as though it were a function as seen before.
var example5method = "Example5 sayIt";
+
class Example5Class {
sayIt() {
print(example5method);
}
}
+
example5() {
- // Create an anonymous instance of the Example5Class and call the sayIt
- // method on it.
+ /// Create an anonymous instance of the Example5Class and call the sayIt
+ /// method on it.
+ /// the `new` keyword is optional in Dart.
new Example5Class().sayIt();
}
-// Class declaration takes the form of class name { [classBody] }.
-// Where classBody can include instance methods and variables, but also
-// class methods and variables.
+/// Class declaration takes the form of class name { [classBody] }.
+/// Where classBody can include instance methods and variables, but also
+/// class methods and variables.
class Example6Class {
var instanceVariable = "Example6 instance variable";
sayIt() {
print(instanceVariable);
}
}
+
example6() {
- new Example6Class().sayIt();
+ 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() {
print(classVariable);
}
+
sayItFromInstance() {
print(classVariable);
}
}
+
example7() {
Example7Class.sayItFromClass();
new Example7Class().sayItFromInstance();
}
-// 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
-// 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
-// declaring them "const".
-var example8Array = const ["Example8 const array"],
- example8Map = const {"someKey": "Example8 const map"};
+/// Dart supports Generics.
+/// Generics refers to the technique of writing the code for a class
+/// without specifying the data type(s) that the class works on.
+/// Source: https://stackoverflow.com/questions/4560890/what-are-generics-in-c
+
+/// Type `T` refers to any type that has been instantiated
+/// you can call whatever you want
+/// Programmers uses the convention in the following
+/// T - Type(used for class and primitype types)
+/// E - Element(used for List, Set, or Iterable)
+/// K,V - Key Value(used for Map)
+class GenericExample<T>{
+ void printType(){
+ print("$T")
+ }
+ // methods can also have generics
+ genericMethod<M>(){
+ print("class:$T, method: $M");
+ }
+}
+
+
+/// List are similar to arrays but list is a child of Iterable<E>
+/// Therefore Maps, List, LinkedList are all child of Iterable<E> to be able to loop using the keyword `for`
+/// Important things to remember:
+/// () - Iterable<E>
+/// [] - List<E>
+/// {} - Map<K,V>
+
+
+/// List are great, but there's a restriction for what List can be
+/// outside of function/method bodies. List on the outer scope of class
+/// 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
+/// declaring them "const". Kind of similar to Javascript's Object.freeze()
+const example8List = ["Example8 const array"],
+const example8Map = {"someKey": "Example8 const map"};
+/// Declare List or Maps as Objects.
+ List<String> explicitList = new List<String>();
+ Map<String,dynamic> explicitMaps = new Map<String,dynamic>();
+
+ explicitList.add("SomeArray");
example8() {
print(example8Array[0]);
print(example8Map["someKey"]);
+ print(explicitList[0]);
}
-// Loops in Dart take the form of standard for () {} or while () {} loops,
-// slightly more modern for (.. in ..) {}, or functional callbacks with many
-// supported features, starting with forEach.
+/// Assigning a list from one variable to another will not be the same result.
+/// Because dart is pass-reference-by-value.
+/// So when you assign an existing list to a new variable.
+/// Instead of List, it becomes an Iterable
+var iterableExplicitList = explicitList;
+print(iterableExplicitList) // ("SomeArray"); "[]" becomes "()"
+var newExplicitLists = explicitList.toList() // Converts Iterable<E> to List<E>
+
+/// Loops in Dart take the form of standard for () {} or while () {} loops,
+/// slightly more modern for (.. in ..) {}, or functional callbacks with many
+/// supported features, starting with forEach,map and where.
var example9Array = const ["a", "b"];
example9() {
- for (var i = 0; i < example9Array.length; i++) {
+ for (final i = 0; i < example9Array.length; i++) {
print("Example9 for loop '${example9Array[i]}'");
}
var i = 0;
@@ -130,13 +232,15 @@ example9() {
print("Example9 while loop '${example9Array[i]}'");
i++;
}
- for (var e in example9Array) {
+ for (final e in example9Array) {
print("Example9 for-in loop '${e}'");
}
+
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 +251,37 @@ example10() {
}
}
-// Int and double are the two supported number formats.
+/// `int`, `double` and `num` are the three supported number formats.
+/// `num` can be either `int` or `double`.
+/// `int` and `double` are children of type `num`
example11() {
var i = 1 + 320, d = 3.2 + 0.01;
+ num myNumDouble = 2.2;
+ num myNumInt = 2;
+ int myInt = 1;
+ double myDouble = 0; // Dart will add decimal prefix, becomes 0.0;
+ myNumDouble = myInt; // valid
+ myNumDouble = myDouble; //valid
+ myNumDouble = myNumInt; //valid
+
+ myNumInt = myInt; // valid
+ myNumInt = myDouble; // valid
+ myNumInt = myNumDouble; // valid
+
+ myInt = myNumDouble; //Error
+ myInt = myDouble; //Error
+ myInt = myNumInt; //valid
+
+ myDouble = myInt; //error
+ myDouble = myNumInt; //valid
+ myDouble = myNumDouble; //valid
+
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 +289,7 @@ example12() {
print("Example12 tomorrow '${now}'");
}
-// Regular expressions are supported.
+/// Regular expressions are supported.
example13() {
var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$");
match(s) {
@@ -172,11 +299,12 @@ example13() {
print("Example13 regexp doesn't match '${s}'");
}
}
+
match(s1);
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 +314,11 @@ 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
- var b;// b is dynamic type
+ /// dynamic typed null can be convert to bool
+ var b;/// b is dynamic type
b = "abc";
try {
if (b) {
@@ -199,35 +327,35 @@ 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
- // if (c) {
- // print("true, c is $c");
- // } else {
- // print("false, c is $c");
- // }
+ /// complie failed
+ /// if (c) {
+ /// print("true, c is $c");
+ /// } else {
+ /// print("false, c is $c");
+ /// }
}
-// try/catch/finally and throw are used for exception handling.
-// throw takes any object as parameter;
+/// try/catch/finally and throw are used for exception handling.
+/// throw takes any object as parameter;
example15() {
try {
try {
throw "Some unexpected error.";
} catch (e) {
print("Example15 an exception: '${e}'");
- throw e; // Re-throw
+ throw e; /// Re-throw
}
} catch (e) {
print("Example15 catch exception being re-thrown: '${e}'");
@@ -236,18 +364,21 @@ example15() {
}
}
-// To be efficient when creating a long string dynamically, use
-// StringBuffer. Or you could join a string array.
+/// To be efficient when creating a long string dynamically, use
+/// StringBuffer. Or you could join a string array.
example16() {
var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e;
- for (e in a) { sb.write(e); }
+ for (e in a) {
+ sb.write(e);
+ }
print("Example16 dynamic string created with "
- "StringBuffer '${sb.toString()}'");
+ "StringBuffer '${sb.toString()}'");
print("Example16 join string array '${a.join()}'");
}
-// Strings can be concatenated by just having string literals next to
-// one another with no further operator needed.
+/// Strings can be concatenated by just having string List next to
+/// one another with no further operator needed.
+
example17() {
print("Example17 "
"concatenate "
@@ -255,44 +386,44 @@ example17() {
"just like that");
}
-// Strings have single-quote or double-quote for delimiters with no
-// actual difference between the two. The given flexibility can be good
-// to avoid the need to escape content that matches the delimiter being
-// used. For example, double-quotes of HTML attributes if the string
-// contains HTML content.
+/// Strings have single-quote or double-quote for delimiters with no
+/// actual difference between the two. The given flexibility can be good
+/// to avoid the need to escape content that matches the delimiter being
+/// used. For example, double-quotes of HTML attributes if the string
+/// 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
-// multiple lines and include line delimiters.
+/// Strings with triple single-quotes or triple double-quotes span
+/// 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.
-// With $ { [expression] }, the return of the expression is interpolated.
-// $ followed by a variable name interpolates the content of that variable.
-// $ can be escaped like so \$ to just add it to the string instead.
+/// Strings have the nice interpolation feature with the $ character.
+/// With $ { [expression] }, the return of the expression is interpolated.
+/// $ followed by a variable name interpolates the content of that variable.
+/// $ can be escaped like so \$ to just add it to the string instead.
example20() {
var s1 = "'\${s}'", s2 = "'\$s'";
print("Example20 \$ interpolation ${s1} or $s2 works.");
}
-// Optional types allow for the annotation of APIs and come to the aid of
-// IDEs so the IDEs can better refactor, auto-complete and check for
-// errors. So far we haven't declared any types and the programs have
-// worked just fine. In fact, types are disregarded during runtime.
-// Types can even be wrong and the program will still be given the
-// benefit of the doubt and be run as though the types didn't matter.
-// There's a runtime parameter that checks for type errors which is
-// the checked mode, which is said to be useful during development time,
-// but which is also slower because of the extra checking and is thus
-// avoided during deployment runtime.
+/// Optional types allow for the annotation of APIs and come to the aid of
+/// IDEs so the IDEs can better refactor, auto-complete and check for
+/// errors. So far we haven't declared any types and the programs have
+/// worked just fine. In fact, types are disregarded during runtime.
+/// Types can even be wrong and the program will still be given the
+/// benefit of the doubt and be run as though the types didn't matter.
+/// There's a runtime parameter that checks for type errors which is
+/// the checked mode, which is said to be useful during development time,
+/// but which is also slower because of the extra checking and is thus
+/// avoided during deployment runtime.
class Example21 {
List<String> _names;
Example21() {
@@ -302,11 +433,13 @@ class Example21 {
set names(List<String> list) {
_names = list;
}
+
int get length => _names.length;
void add(String name) {
_names.add(name);
}
}
+
void example21() {
Example21 o = new Example21();
o.add("c");
@@ -315,46 +448,50 @@ void example21() {
print("Example21 names '${o.names}' and length '${o.length}'");
}
-// Class inheritance takes the form of class name extends AnotherClassName {}.
+/// Class inheritance takes the form of class name extends AnotherClassName {}.
class Example22A {
var _name = "Some Name!";
get name => _name;
}
+
class Example22B extends Example22A {}
+
example22() {
var o = new Example22B();
print("Example22 class inheritance '${o.name}'");
}
-// Class mixin is also available, and takes the form of
-// class name extends SomeClass with AnotherClassName {}.
-// 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.
-// Mixin is mostly used to share methods with distant classes, so the
-// single inheritance doesn't get in the way of reusable code.
-// Mixins follow the "with" statement during the class declaration.
+/// Class mixin is also available, and takes the form of
+/// class name extends SomeClass with AnotherClassName {}.
+/// 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.
+/// Mixin is mostly used to share methods with distant classes, so the
+/// single inheritance doesn't get in the way of reusable code.
+/// Mixins follow the "with" statement during the class declaration.
class Example23A {}
+
class Example23Utils {
addTwo(n1, n2) {
return n1 + n2;
}
}
+
class Example23B extends Example23A with Example23Utils {
addThree(n1, n2, n3) {
return addTwo(n1, n2) + n3;
}
}
+
example23() {
- var o = new Example23B(), r1 = o.addThree(1, 2, 3),
- r2 = o.addTwo(1, 2);
+ var o = new Example23B(), r1 = o.addThree(1, 2, 3), r2 = o.addTwo(1, 2);
print("Example23 addThree(1, 2, 3) results in '${r1}'");
print("Example23 addTwo(1, 2) results in '${r2}'");
}
-// The Class constructor method uses the same name of the class and
-// takes the form of SomeClass() : super() {}, where the ": super()"
-// part is optional and it's used to delegate constant parameters to the
-// super-parent's constructor.
+/// The Class constructor method uses the same name of the class and
+/// takes the form of SomeClass() : super() {}, where the ": super()"
+/// part is optional and it's used to delegate constant parameters to the
+/// super-parent's constructor.
class Example24A {
var _value;
Example24A({value: "someValue"}) {
@@ -362,71 +499,76 @@ class Example24A {
}
get value => _value;
}
+
class Example24B extends Example24A {
Example24B({value: "someOtherValue"}) : super(value: value);
}
+
example24() {
- var o1 = new Example24B(),
- o2 = new Example24B(value: "evenMore");
+ var o1 = new Example24B(), o2 = new Example24B(value: "evenMore");
print("Example24 calling super during constructor '${o1.value}'");
print("Example24 calling super during constructor '${o2.value}'");
}
-// 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
-// an instance variable of same name.
+/// 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
+/// an instance variable of same name.
class Example25 {
var value, anotherValue;
Example25({this.value, this.anotherValue});
}
+
example25() {
var o = new Example25(value: "a", anotherValue: "b");
print("Example25 shortcut for constructor '${o.value}' and "
- "'${o.anotherValue}'");
+ "'${o.anotherValue}'");
}
-// Named parameters are available when declared between {}.
-// Parameter order can be optional when declared between {}.
-// Parameters can be made optional when declared between [].
+/// Named parameters are available when declared between {}.
+/// Parameter order can be optional when declared between {}.
+/// Parameters can be made optional when declared between [].
example26() {
var _name, _surname, _email;
setConfig1({name, surname}) {
_name = name;
_surname = surname;
}
+
setConfig2(name, [surname, email]) {
_name = name;
_surname = surname;
_email = email;
}
+
setConfig1(surname: "Doe", name: "John");
print("Example26 name '${_name}', surname '${_surname}', "
- "email '${_email}'");
+ "email '${_email}'");
setConfig2("Mary", "Jane");
print("Example26 name '${_name}', surname '${_surname}', "
- "email '${_email}'");
+ "email '${_email}'");
}
-// Variables declared with final can only be set once.
-// In case of classes, final instance variables can be set via constant
-// constructor parameter.
+/// Variables declared with final can only be set once.
+/// In case of classes, final instance variables can be set via constant
+/// constructor parameter.
class Example27 {
final color1, color2;
- // A little flexibility to set final instance variables with syntax
- // that follows the :
+ /// A little flexibility to set final instance variables with syntax
+ /// that follows the :
Example27({this.color1, color2}) : color2 = color2;
}
+
example27() {
final color = "orange", o = new Example27(color1: "lilac", color2: "white");
print("Example27 color is '${color}'");
print("Example27 color is '${o.color1}' and '${o.color2}'");
}
-// 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
-// its own convention of import "package:packageName".
-// See import "dart:collection"; at the top. Imports must come before
-// other code declarations. IterableBase comes from dart:collection.
+/// 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
+/// its own convention of import "package:packageName".
+/// See import "dart:collection"; at the top. Imports must come before
+/// other code declarations. IterableBase comes from dart:collection.
class Example28 extends IterableBase {
var names;
Example28() {
@@ -434,16 +576,17 @@ class Example28 extends IterableBase {
}
get iterator => names.iterator;
}
+
example28() {
var o = new Example28();
o.forEach((name) => print("Example28 '${name}'"));
}
-// For control flow we have:
-// * standard switch with must break statements
-// * if-else if-else and ternary ..?..:.. operator
-// * closures and anonymous functions
-// * break, continue and return statements
+/// For control flow we have:
+/// * standard switch with must break statements
+/// * if-else if-else and ternary ..?..:.. operator
+/// * closures and anonymous functions
+/// * break, continue and return statements
example29() {
var v = true ? 30 : 60;
switch (v) {
@@ -459,10 +602,12 @@ example29() {
callItForMe(fn()) {
return fn();
}
+
rand() {
v = new DM.Random().nextInt(50);
return v;
}
+
while (true) {
print("Example29 callItForMe(rand) '${callItForMe(rand)}'");
if (v != 30) {
@@ -470,17 +615,21 @@ example29() {
} else {
continue;
}
- // Never gets here.
+ /// Never gets here.
}
}
-// Parse int, convert double to int, or just keep int when dividing numbers
-// by using the ~/ operation. Let's play a guess game too.
+/// Parse int, convert double to int, or just keep int when dividing numbers
+/// 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;
+ 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) {
@@ -488,10 +637,11 @@ example30() {
} else {
tooHigh = n > gn;
print("Example30 Number ${n} is too "
- "${tooHigh ? 'high' : 'low'}. Try again");
+ "${tooHigh ? 'high' : 'low'}. Try again");
}
return n == gn;
}
+
n = (top - bottom) ~/ 2;
while (!guessNumber(n)) {
if (tooHigh) {
@@ -503,19 +653,65 @@ example30() {
}
}
-// Programs have only one entry point in the main function.
-// Nothing is expected to be executed on the outer scope before a program
-// starts running with what's in its main function.
-// This helps with faster loading and even lazily loading of just what
-// the program needs to startup with.
+/// Optional Positional Parameter:
+/// 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');
+ }
+
+ findVolume31(10,20,30); //valid
+ findVolume31(10,20); //also valid
+}
+
+/// Optional Named Parameter:
+/// parameter will be disclosed with curly bracket { }
+/// curly bracketed parameter are optional.
+/// have to use parameter name to assign a value which separated with colan :
+/// 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.
+example32() {
+ findVolume32(int length, int breath, {int height}) {
+ print('length = $length, breath = $breath, height = $height');
+ }
+
+ findVolume32(10,20,height:30);//valid & we can see the parameter name is mentioned here.
+ findVolume32(10,20);//also valid
+}
+
+/// Optional Default 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.
+example33() {
+ findVolume33(int length, int breath, {int height=10}) {
+ print('length = $length, breath = $breath, height = $height');
+ }
+
+ findVolume33(10,20,height:30);//valid
+ findVolume33(10,20);//valid
+}
+
+/// Dart has also added feature such as Null aware operators
+var isBool = true;
+var hasString = isBool ?? "default String";
+var hasValue ??= "default Value";
+
+/// Programs have only one entry point in the main function.
+/// Nothing is expected to be executed on the outer scope before a program
+/// starts running with what's in its main function.
+/// This helps with faster loading and even lazily loading of just what
+/// the program needs to startup with.
main() {
print("Learn Dart in 15 minutes!");
- [example1, example2, example3, example4, example5, example6, example7,
- example8, example9, example10, example11, example12, example13, example14,
- example15, example16, example17, example18, example19, example20,
- example21, example22, example23, example24, example25, example26,
- example27, example28, example29, example30
- ].forEach((ef) => ef());
+ [
+ example1, example2, example3, example4, example5,
+ example6, example7, example8, example9, example10,
+ example11, example12, example13, example14, example15,
+ example16, example17, example18, example19, example20,
+ example21, example22, example23, example24, example25,
+ example26, example27, example28, example29,
+ example30 // Adding this comment stops the dart formatter from putting all items on a new line
+ ].forEach((ef) => ef());
}
```
@@ -526,6 +722,3 @@ 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)
-
-
-