diff options
Diffstat (limited to 'dart.html.markdown')
| -rw-r--r-- | dart.html.markdown | 577 |
1 files changed, 396 insertions, 181 deletions
diff --git a/dart.html.markdown b/dart.html.markdown index fc7b220e..b215474a 100644 --- a/dart.html.markdown +++ b/dart.html.markdown @@ -2,159 +2,285 @@ 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 purpose programming language. +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). -```javascript +```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() { - example1nested1() { - example1nested2() => print("Example1 nested 1 nested 2"); - example1nested2(); + nested1() { + nested2() => print("Example1 nested 1 nested 2"); + nested2(); } - example1nested1(); + + nested1(); } -// Anonymous functions don't include a name. +/// Anonymous functions don't include a name but can take number of arguments example2() { - example2nested1(fn) { + //// Explicit return type. + nested1(Function<void> fn) { fn(); } - example2nested1(() => print("Example2 nested 1")); + + 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() { - example3nested1(fn(informSomething)) { - fn("Example3 nested 1"); + planA(fn(String informSomething)) { + fn("Example3 plan A"); } - example3planB(fn) { // Or don't declare number of parameters. + planB(fn) { + // Or don't declare number of parameters. fn("Example3 plan B"); } - example3nested1((s) => print(s)); - example3planB((s) => print(s)); + + 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() { - example4nested1(fn(informSomething)) { + nested1(fn(informSomething)) { fn(example4Something); } - example4nested1((s) => print(s)); + + 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 example6InstanceVariable = "Example6 instance variable"; + var instanceVariable = "Example6 instance variable"; sayIt() { - print(example6InstanceVariable); + 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 example7ClassVariable = "Example7 class variable"; + static var classVariable = "Example7 class variable"; static sayItFromClass() { - print(example7ClassVariable); + print(classVariable); } + sayItFromInstance() { - print(example7ClassVariable); + 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 example8A = const ["Example8 const array"], - example8M = const {"someKey": "Example8 const map"}; -example8() { - print(example8A[0]); - print(example8M["someKey"]); +/// 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"); + } } -// 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. -var example9A = const ["a", "b"]; + +/// 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(example8Map["someKey"]); + print(explicitList[0]); +} + +/// 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 < example9A.length; i++) { - print("Example9 for loop '${example9A[i]}'"); + for (int i = 0; i < example9Array.length; i++) { + print("Example9 for loop '${example9Array[i]}'"); } var i = 0; - while (i < example9A.length) { - print("Example9 while loop '${example9A[i]}'"); + while (i < example9Array.length) { + print("Example9 while loop '${example9Array[i]}'"); i++; } - for (var e in example9A) { + for (final e in example9Array) { print("Example9 for-in loop '${e}'"); } - example9A.forEach((e) => print("Example9 forEach loop '${e}'")); + + example9Array.forEach((e) => print("Example9 forEach loop '${e}'")); + } -// To loop over the characters of a string or to extract a substring. -var example10S = "ab"; +/// To loop over the characters of a string or to extract a substring. +var example10String = "ab"; example10() { - for (var i = 0; i < example10S.length; i++) { - print("Example10 String character loop '${example10S[i]}'"); + for (var i = 0; i < example10String.length; i++) { + print("Example10 String character loop '${example10String[i]}'"); } - for (var i = 0; i < example10S.length; i++) { - print("Example10 substring loop '${example10S.substring(i, i + 1)}'"); + for (var i = 0; i < example10String.length; i++) { + print("Example10 substring loop '${example10String.substring(i, i + 1)}'"); } } -// 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 +288,7 @@ example12() { print("Example12 tomorrow '${now}'"); } -// Regular expressions are supported. +/// Regular expressions are supported. example13() { var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$"); match(s) { @@ -172,38 +298,63 @@ example13() { print("Example13 regexp doesn't match '${s}'"); } } + match(s1); match(s2); } -// Boolean expressions need to resolve to either true or false, as no -// implicit conversions are supported. +/// Boolean expressions support implicit conversions and dynamic type example14() { - var v = true; - if (v) { - print("Example14 value is true"); + var a = true; + if (a) { + print("true, a is $a"); } - v = null; + a = null; + if (a) { + print("true, a is $a"); + } else { + print("false, a is $a"); /// runs here + } + + /// dynamic typed null can be convert to bool + var b;/// b is dynamic type + b = "abc"; try { - if (v) { - // Never runs + if (b) { + print("true, b is $b"); } else { - // Never runs + print("false, b is $b"); } } catch (e) { - print("Example14 null value causes an exception: '${e}'"); + 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 } + + /// 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 $c"); + /// } } -// try/catch/finally and throw are used for exception handling. -// throw takes any object as parameter; +/// try/catch/finally and throw are used for exception handling. +/// throw takes any object as parameter; example15() { try { try { throw "Some unexpected error."; } catch (e) { print("Example15 an exception: '${e}'"); - throw e; // Re-throw + throw e; /// Re-throw } } catch (e) { print("Example15 catch exception being re-thrown: '${e}'"); @@ -212,18 +363,21 @@ example15() { } } -// To be efficient when creating a long string dynamically, use -// StringBuffer. Or you could join a string array. +/// To be efficient when creating a long string dynamically, use +/// StringBuffer. Or you could join a string array. example16() { var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e; - for (e in a) { sb.write(e); } + for (e in a) { + sb.write(e); + } print("Example16 dynamic string created with " - "StringBuffer '${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 " @@ -231,44 +385,44 @@ 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 $s2 works."); } -// Optional types allow for the annotation of APIs and come to the aid of -// IDEs so the IDEs can better refactor, auto-complete and check for -// errors. So far we haven't declared any types and the programs have -// worked just fine. In fact, types are disregarded during runtime. -// Types can even be wrong and the program will still be given the -// benefit of the doubt and be run as though the types didn't matter. -// There's a runtime parameter that checks for type errors which is -// the checked mode, which is said to be useful during development time, -// but which is also slower because of the extra checking and is thus -// avoided during deployment runtime. +/// Optional types allow for the annotation of APIs and come to the aid of +/// IDEs so the IDEs can better refactor, auto-complete and check for +/// errors. So far we haven't declared any types and the programs have +/// worked just fine. In fact, types are disregarded during runtime. +/// Types can even be wrong and the program will still be given the +/// benefit of the doubt and be run as though the types didn't matter. +/// There's a runtime parameter that checks for type errors which is +/// the checked mode, which is said to be useful during development time, +/// but which is also slower because of the extra checking and is thus +/// avoided during deployment runtime. class Example21 { List<String> _names; Example21() { @@ -278,11 +432,13 @@ class Example21 { set names(List<String> list) { _names = list; } + int get length => _names.length; void add(String name) { _names.add(name); } } + void example21() { Example21 o = new Example21(); o.add("c"); @@ -291,46 +447,50 @@ void example21() { print("Example21 names '${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"}) { @@ -338,71 +498,76 @@ 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() { @@ -410,16 +575,17 @@ class Example28 extends IterableBase { } get iterator => names.iterator; } + example28() { var o = new Example28(); o.forEach((name) => print("Example28 '${name}'")); } -// For control flow we have: -// * standard switch with must break statements -// * if-else if-else and ternary ..?..:.. operator -// * closures and anonymous functions -// * break, continue and return statements +/// For control flow we have: +/// * standard switch with must break statements +/// * if-else if-else and ternary ..?..:.. operator +/// * closures and anonymous functions +/// * break, continue and return statements example29() { var v = true ? 30 : 60; switch (v) { @@ -435,10 +601,12 @@ example29() { callItForMe(fn()) { return fn(); } + rand() { v = new DM.Random().nextInt(50); return v; } + while (true) { print("Example29 callItForMe(rand) '${callItForMe(rand)}'"); if (v != 30) { @@ -446,17 +614,21 @@ 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) { @@ -464,10 +636,11 @@ 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) { @@ -479,19 +652,64 @@ 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"; + +/// 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()); } ``` @@ -500,8 +718,5 @@ main() { Dart has a comprehensive web-site. It covers API reference, tutorials, articles and more, including a useful Try Dart online. -http://www.dartlang.org/ -http://try.dartlang.org/ - - - +[https://www.dartlang.org](https://www.dartlang.org) +[https://try.dartlang.org](https://try.dartlang.org) |