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Merge pull request #3820 from ram231/master
[dart/en] Update Guide and add more features
This commit is contained in:
Divay Prakash
GitHub
commit
e440903935
@ -2,28 +2,72 @@
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language: dart
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filename: learndart.dart
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contributors:
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- ["Joao Pedrosa", "https://github.com/jpedrosa/"]
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- ["Joao Pedrosa", "https://github.com/jpedrosa/"]
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- ["Vince Ramces Oliveros", "https://github.com/ram231"]
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---
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Dart is a newcomer into the realm of programming languages.
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It borrows a lot from other mainstream languages, having as a goal not to deviate too much from
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its JavaScript sibling. Like JavaScript, Dart aims for great browser integration.
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**Dart** is a single threaded, general puprose programming languages.
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It borrows a lot from other mainstream languages.
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It supports Streams, Futures(known as Promises in JavaScript), Generics, First-class functions(closures) and static type checking.
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Dart can run in any platform such as Web, CLI, Desktop, Mobile and IoT devices.
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Dart's most controversial feature must be its Optional Typing.
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Dart's most controversial feature is its ~~Optional Typing~~ Static Type safety and [Sound Type checks](https://dart.dev/guides/language/sound-dart).
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```dart
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import "dart:collection";
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import "dart:math" as DM;
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import "dart:math" as math;
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// Welcome to Learn Dart in 15 minutes. http://www.dartlang.org/
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// This is an executable tutorial. You can run it with Dart or on
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// the Try Dart! site if you copy/paste it there. http://try.dartlang.org/
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/// Welcome to Learn Dart in 15 minutes. http://dart.dev/
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/// This is an executable tutorial. You can run it with Dart or on
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/// the Try Dart! site if you copy/paste it there. http://dartpad.dev/
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/// You can also run Flutter in DartPad by click the `< > New Pad ` and choose Flutter
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// Function declaration and method declaration look the same. Function
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// declarations can be nested. The declaration takes the form of
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// name() {} or name() => singleLineExpression;
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// The fat arrow function declaration has an implicit return for the result of
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// the expression.
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/// In Dart, Everything is an Object.
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/// Every declaration of an object is an instance of Null and
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/// Null is also an object.
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/// 3 Types of comments in dart
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// Single line comment
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/**
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* Multi-line comment
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* Can comment more than 2 lines
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*/
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/// Code doc comment
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/// It uses markdown syntax to generate code docs when making an API.
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/// Code doc comment is the recommended choice when documenting your APIs, classes and methods.
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/// 4 types of variable declaration.
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/// Constants are variables that are immutable cannot be change or altered.
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/// `const` in dart should practice SCREAMING_SNAKE_CASE name declaration.
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const CONSTANT_VALUE = "I CANNOT CHANGE";
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CONSTANT_VALUE = "DID I?"; //Error
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/// Final is another variable declaration that cannot be change once it has been instantiated. Commonly used in classes and functions
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/// `final` can be declared in pascalCase.
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final finalValue = "value cannot be change once instantiated";
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finalValue = "Seems not"; //Error
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/// `var` is another variable declaration that is mutable and can change its value. Dart will infer types and will not change its data type
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var mutableValue = "Variable string";
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mutableValue = "this is valid";
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mutableValue = false; // Error.
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/// `dynamic` is another variable declaration in which the type is not evaluated by the dart static type checking.
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/// It can change its value and data type.
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/// Some dartisans uses dynamic cautiously as it cannot keep track of its data type. so use it at your own risk
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dynamic dynamicValue = "I'm a string";
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dynamicValue = false; // false
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/// Functions can be declared in a global space
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/// Function declaration and method declaration look the same. Function
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/// declarations can be nested. The declaration takes the form of
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/// name() {} or name() => singleLineExpression;
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/// The fat arrow function declaration can be an implicit or
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/// explicit return for the result of the expression.
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/// Dart will execute a function called `main()` anywhere in the dart project.
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///
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example1() {
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nested1() {
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nested2() => print("Example1 nested 1 nested 2");
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@ -33,23 +77,23 @@ example1() {
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nested1();
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}
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// Anonymous functions don't include a name.
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/// Anonymous functions don't include a name but can take number of arguments
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example2() {
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nested1(fn) {
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//// Explicit return type.
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nested1(Function<void> fn) {
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fn();
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}
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nested1(() => print("Example2 nested 1"));
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}
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// When a function parameter is declared, the declaration can include the
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// number of parameters the function takes by specifying the names of the
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// parameters it takes.
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/// When a function parameter is declared, the declaration can include the
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/// number of parameters the function takes by explicitly specifying the names of the
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/// parameters it takes.
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example3() {
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planA(fn(informSomething)) {
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planA(fn(String informSomething)) {
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fn("Example3 plan A");
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}
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planB(fn) {
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// Or don't declare number of parameters.
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fn("Example3 plan B");
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@ -59,7 +103,9 @@ example3() {
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planB((s) => print(s));
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}
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// Functions have closure access to outer variables.
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/// Functions have closure access to outer variables.
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/// Dart will infer types when the variable has a value of something.
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/// In this example dart knows that this variable is a String.
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var example4Something = "Example4 nested 1";
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example4() {
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nested1(fn(informSomething)) {
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@ -69,8 +115,8 @@ example4() {
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nested1((s) => print(s));
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}
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// Class declaration with a sayIt method, which also has closure access
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// to the outer variable as though it were a function as seen before.
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/// Class declaration with a sayIt method, which also has closure access
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/// to the outer variable as though it were a function as seen before.
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var example5method = "Example5 sayIt";
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class Example5Class {
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@ -80,14 +126,15 @@ class Example5Class {
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}
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example5() {
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// Create an anonymous instance of the Example5Class and call the sayIt
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// method on it.
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/// Create an anonymous instance of the Example5Class and call the sayIt
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/// method on it.
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/// the `new` keyword is optional in Dart.
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new Example5Class().sayIt();
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}
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// Class declaration takes the form of class name { [classBody] }.
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// Where classBody can include instance methods and variables, but also
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// class methods and variables.
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/// Class declaration takes the form of class name { [classBody] }.
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/// Where classBody can include instance methods and variables, but also
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/// class methods and variables.
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class Example6Class {
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var instanceVariable = "Example6 instance variable";
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sayIt() {
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@ -96,10 +143,10 @@ class Example6Class {
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}
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example6() {
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new Example6Class().sayIt();
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Example6Class().sayIt();
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}
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// Class methods and variables are declared with "static" terms.
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/// Class methods and variables are declared with "static" terms.
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class Example7Class {
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static var classVariable = "Example7 class variable";
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static sayItFromClass() {
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@ -116,24 +163,68 @@ example7() {
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new Example7Class().sayItFromInstance();
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}
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// Literals are great, but there's a restriction for what literals can be
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// outside of function/method bodies. Literals on the outer scope of class
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// or outside of class have to be constant. Strings and numbers are constant
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// by default. But arrays and maps are not. They can be made constant by
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// declaring them "const".
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var example8Array = const ["Example8 const array"],
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example8Map = const {"someKey": "Example8 const map"};
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/// Dart supports Generics.
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/// Generics refers to the technique of writing the code for a class
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/// without specifying the data type(s) that the class works on.
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/// Source: https://stackoverflow.com/questions/4560890/what-are-generics-in-c
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/// Type `T` refers to any type that has been instantiated
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/// you can call whatever you want
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/// Programmers uses the convention in the following
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/// T - Type(used for class and primitype types)
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/// E - Element(used for List, Set, or Iterable)
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/// K,V - Key Value(used for Map)
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class GenericExample<T>{
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void printType(){
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print("$T")
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}
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// methods can also have generics
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genericMethod<M>(){
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print("class:$T, method: $M");
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}
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}
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/// List are similar to arrays but list is a child of Iterable<E>
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/// Therefore Maps, List, LinkedList are all child of Iterable<E> to be able to loop using the keyword `for`
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/// Important things to remember:
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/// () - Iterable<E>
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/// [] - List<E>
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/// {} - Map<K,V>
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/// List are great, but there's a restriction for what List can be
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/// outside of function/method bodies. List on the outer scope of class
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/// or outside of class have to be constant. Strings and numbers are constant
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/// by default. But arrays and maps are not. They can be made constant by
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/// declaring them "const". Kind of similar to Javascript's Object.freeze()
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const example8List = ["Example8 const array"],
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const example8Map = {"someKey": "Example8 const map"};
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/// Declare List or Maps as Objects.
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List<String> explicitList = new List<String>();
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Map<String,dynamic> explicitMaps = new Map<String,dynamic>();
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explicitList.add("SomeArray");
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example8() {
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print(example8Array[0]);
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print(example8Map["someKey"]);
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print(explicitList[0]);
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}
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// Loops in Dart take the form of standard for () {} or while () {} loops,
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// slightly more modern for (.. in ..) {}, or functional callbacks with many
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// supported features, starting with forEach.
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/// Assigning a list from one variable to another will not be the same result.
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/// Because dart is pass-reference-by-value.
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/// So when you assign an existing list to a new variable.
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/// Instead of List, it becomes an Iterable
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var iterableExplicitList = explicitList;
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print(iterableExplicitList) // ("SomeArray"); "[]" becomes "()"
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var newExplicitLists = explicitList.toList() // Converts Iterable<E> to List<E>
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/// Loops in Dart take the form of standard for () {} or while () {} loops,
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/// slightly more modern for (.. in ..) {}, or functional callbacks with many
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/// supported features, starting with forEach,map and where.
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var example9Array = const ["a", "b"];
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example9() {
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for (var i = 0; i < example9Array.length; i++) {
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for (final i = 0; i < example9Array.length; i++) {
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print("Example9 for loop '${example9Array[i]}'");
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}
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var i = 0;
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@ -141,13 +232,15 @@ example9() {
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print("Example9 while loop '${example9Array[i]}'");
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i++;
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}
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for (var e in example9Array) {
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for (final e in example9Array) {
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print("Example9 for-in loop '${e}'");
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}
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example9Array.forEach((e) => print("Example9 forEach loop '${e}'"));
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}
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// To loop over the characters of a string or to extract a substring.
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/// To loop over the characters of a string or to extract a substring.
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var example10String = "ab";
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example10() {
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for (var i = 0; i < example10String.length; i++) {
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@ -158,14 +251,37 @@ example10() {
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}
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}
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// Int and double are the two supported number formats.
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/// `int`, `double` and `num` are the three supported number formats.
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/// `num` can be either `int` or `double`.
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/// `int` and `double` are children of type `num`
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example11() {
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var i = 1 + 320, d = 3.2 + 0.01;
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num myNumDouble = 2.2;
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num myNumInt = 2;
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int myInt = 1;
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double myDouble = 0; // Dart will add decimal prefix, becomes 0.0;
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myNumDouble = myInt; // valid
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myNumDouble = myDouble; //valid
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myNumDouble = myNumInt; //valid
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myNumInt = myInt; // valid
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myNumInt = myDouble; // valid
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myNumInt = myNumDouble; // valid
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myInt = myNumDouble; //Error
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myInt = myDouble; //Error
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myInt = myNumInt; //valid
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myDouble = myInt; //error
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myDouble = myNumInt; //valid
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myDouble = myNumDouble; //valid
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print("Example11 int ${i}");
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print("Example11 double ${d}");
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}
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// DateTime provides date/time arithmetic.
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/// DateTime provides date/time arithmetic.
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example12() {
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var now = new DateTime.now();
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print("Example12 now '${now}'");
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@ -173,7 +289,7 @@ example12() {
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print("Example12 tomorrow '${now}'");
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}
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// Regular expressions are supported.
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/// Regular expressions are supported.
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example13() {
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var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$");
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match(s) {
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@ -188,7 +304,7 @@ example13() {
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match(s2);
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}
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// Boolean expressions support implicit conversions and dynamic type
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/// Boolean expressions support implicit conversions and dynamic type
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example14() {
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var a = true;
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if (a) {
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@ -198,11 +314,11 @@ example14() {
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if (a) {
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print("true, a is $a");
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} else {
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print("false, a is $a"); // runs here
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print("false, a is $a"); /// runs here
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}
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// dynamic typed null can be convert to bool
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var b; // b is dynamic type
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/// dynamic typed null can be convert to bool
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var b;/// b is dynamic type
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b = "abc";
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try {
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if (b) {
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@ -211,35 +327,35 @@ example14() {
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print("false, b is $b");
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}
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} catch (e) {
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print("error, b is $b"); // this could be run but got error
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print("error, b is $b"); /// this could be run but got error
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}
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b = null;
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if (b) {
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print("true, b is $b");
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} else {
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print("false, b is $b"); // runs here
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print("false, b is $b"); /// runs here
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}
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// statically typed null can not be convert to bool
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/// statically typed null can not be convert to bool
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var c = "abc";
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c = null;
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// compile failed
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// if (c) {
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// print("true, c is $c");
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// } else {
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// print("false, c is $c");
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// }
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/// complie failed
|
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/// if (c) {
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/// print("true, c is $c");
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/// } else {
|
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/// print("false, c is $c");
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/// }
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}
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// try/catch/finally and throw are used for exception handling.
|
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// throw takes any object as parameter;
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/// try/catch/finally and throw are used for exception handling.
|
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/// throw takes any object as parameter;
|
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example15() {
|
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try {
|
||||
try {
|
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throw "Some unexpected error.";
|
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} catch (e) {
|
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print("Example15 an exception: '${e}'");
|
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throw e; // Re-throw
|
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throw e; /// Re-throw
|
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}
|
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} catch (e) {
|
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print("Example15 catch exception being re-thrown: '${e}'");
|
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@ -248,8 +364,8 @@ example15() {
|
||||
}
|
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}
|
||||
|
||||
// To be efficient when creating a long string dynamically, use
|
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// StringBuffer. Or you could join a string array.
|
||||
/// To be efficient when creating a long string dynamically, use
|
||||
/// StringBuffer. Or you could join a string array.
|
||||
example16() {
|
||||
var sb = new StringBuffer(), a = ["a", "b", "c", "d"], e;
|
||||
for (e in a) {
|
||||
@ -260,8 +376,9 @@ example16() {
|
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print("Example16 join string array '${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 "
|
||||
@ -269,44 +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 $s2 works.");
|
||||
}
|
||||
|
||||
// Optional types allow for the annotation of APIs and come to the aid of
|
||||
// IDEs so the IDEs can better refactor, auto-complete and check for
|
||||
// errors. So far we haven't declared any types and the programs have
|
||||
// worked just fine. In fact, types are disregarded during runtime.
|
||||
// Types can even be wrong and the program will still be given the
|
||||
// benefit of the doubt and be run as though the types didn't matter.
|
||||
// There's a runtime parameter that checks for type errors which is
|
||||
// the checked mode, which is said to be useful during development time,
|
||||
// but which is also slower because of the extra checking and is thus
|
||||
// avoided during deployment runtime.
|
||||
/// Optional types allow for the annotation of APIs and come to the aid of
|
||||
/// IDEs so the IDEs can better refactor, auto-complete and check for
|
||||
/// errors. So far we haven't declared any types and the programs have
|
||||
/// worked just fine. In fact, types are disregarded during runtime.
|
||||
/// Types can even be wrong and the program will still be given the
|
||||
/// benefit of the doubt and be run as though the types didn't matter.
|
||||
/// There's a runtime parameter that checks for type errors which is
|
||||
/// the checked mode, which is said to be useful during development time,
|
||||
/// but which is also slower because of the extra checking and is thus
|
||||
/// avoided during deployment runtime.
|
||||
class Example21 {
|
||||
List<String> _names;
|
||||
Example21() {
|
||||
@ -331,7 +448,7 @@ void example21() {
|
||||
print("Example21 names '${o.names}' and length '${o.length}'");
|
||||
}
|
||||
|
||||
// Class inheritance takes the form of class name extends AnotherClassName {}.
|
||||
/// Class inheritance takes the form of class name extends AnotherClassName {}.
|
||||
class Example22A {
|
||||
var _name = "Some Name!";
|
||||
get name => _name;
|
||||
@ -344,13 +461,13 @@ example22() {
|
||||
print("Example22 class inheritance '${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 {
|
||||
@ -371,10 +488,10 @@ example23() {
|
||||
print("Example23 addTwo(1, 2) results in '${r2}'");
|
||||
}
|
||||
|
||||
// The Class constructor method uses the same name of the class and
|
||||
// takes the form of SomeClass() : super() {}, where the ": super()"
|
||||
// part is optional and it's used to delegate constant parameters to the
|
||||
// super-parent's constructor.
|
||||
/// The Class constructor method uses the same name of the class and
|
||||
/// takes the form of SomeClass() : super() {}, where the ": super()"
|
||||
/// part is optional and it's used to delegate constant parameters to the
|
||||
/// super-parent's constructor.
|
||||
class Example24A {
|
||||
var _value;
|
||||
Example24A({value: "someValue"}) {
|
||||
@ -393,9 +510,9 @@ example24() {
|
||||
print("Example24 calling super during constructor '${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});
|
||||
@ -407,9 +524,9 @@ example25() {
|
||||
"'${o.anotherValue}'");
|
||||
}
|
||||
|
||||
// Named parameters are available when declared between {}.
|
||||
// Parameter order can be optional when declared between {}.
|
||||
// Parameters can be made optional when declared between [].
|
||||
/// Named parameters are available when declared between {}.
|
||||
/// Parameter order can be optional when declared between {}.
|
||||
/// Parameters can be made optional when declared between [].
|
||||
example26() {
|
||||
var _name, _surname, _email;
|
||||
setConfig1({name, surname}) {
|
||||
@ -431,13 +548,13 @@ example26() {
|
||||
"email '${_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;
|
||||
}
|
||||
|
||||
@ -447,11 +564,11 @@ example27() {
|
||||
print("Example27 color is '${o.color1}' and '${o.color2}'");
|
||||
}
|
||||
|
||||
// To import a library, use import "libraryPath" or if it's a core library,
|
||||
// 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() {
|
||||
@ -465,11 +582,11 @@ 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) {
|
||||
@ -498,12 +615,12 @@ 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,
|
||||
@ -512,7 +629,7 @@ example30() {
|
||||
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) {
|
||||
@ -536,8 +653,8 @@ example30() {
|
||||
}
|
||||
}
|
||||
|
||||
// Optional Positional Parameter:
|
||||
// parameter will be disclosed with square bracket [ ] & square bracketed parameter are optional.
|
||||
/// 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');
|
||||
@ -547,12 +664,12 @@ example31() {
|
||||
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.
|
||||
/// 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');
|
||||
@ -562,23 +679,28 @@ example32() {
|
||||
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.
|
||||
/// 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
|
||||
findVolume33(10,20);//valid
|
||||
}
|
||||
|
||||
// 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.
|
||||
/// 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!");
|
||||
[
|
||||
|
||||
Loading…
Reference in New Issue
Block a user