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diff --git a/dart.html.markdown b/dart.html.markdown new file mode 100644 index 00000000..dc228d16 --- /dev/null +++ b/dart.html.markdown @@ -0,0 +1,506 @@ +--- +language: Dart +author: Joao Pedrosa +author_url: github.com/jpedrosa/ +--- + +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's most controversial feature must be its Optional Typing. + +```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. +example1() { + example1nested1() { + example1nested2() => print("Example1 nested 1 nested 2"); + example1nested2(); + } + example1nested1(); +} + +// Anonymous functions don't include a name. +example2() { + example2nested1(fn) { + fn(); + } + example2nested1(() => 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. +example3() { + example3nested1(fn(informSomething)) { + fn("Example3 nested 1"); + } + example3planB(fn) { // Or don't declare number of parameters. + fn("Example3 plan B"); + } + example3nested1((s) => print(s)); + example3planB((s) => print(s)); +} + +// Functions have closure access to outer variables. +var example4Something = "Example4 nested 1"; +example4() { + example4nested1(fn(informSomething)) { + fn(example4Something); + } + example4nested1((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. +var example5method = "Example5 sayIt"; +class Example5Class { + sayIt() { + print(example5method); + } +} +example5() { + // Create an anonymous instance of the Example5Class and call the sayIt + // method on it. + 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 Example6Class { + var example6InstanceVariable = "Example6 instance variable"; + sayIt() { + print(example6InstanceVariable); + } +} +example6() { + new Example6Class().sayIt(); +} + +// Class methods and variables are declared with "static" terms. +class Example7Class { + static var example7ClassVariable = "Example7 class variable"; + static sayItFromClass() { + print(example7ClassVariable); + } + sayItFromInstance() { + print(example7ClassVariable); + } +} +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"]); +} + +// 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"]; +example9() { + for (var i = 0; i < example9A.length; i++) { + print("Example9 for loop '${example9A[i]}'"); + } + var i = 0; + while (i < example9A.length) { + print("Example9 while loop '${example9A[i]}'"); + i++; + } + for (var e in example9A) { + print("Example9 for-in loop '${e}'"); + } + example9A.forEach((e) => print("Example9 forEach loop '${e}'")); +} + +// To loop over the characters of a string or to extract a substring. +var example10S = "ab"; +example10() { + for (var i = 0; i < example10S.length; i++) { + print("Example10 String character loop '${example10S[i]}'"); + } + for (var i = 0; i < example10S.length; i++) { + print("Example10 substring loop '${example10S.substring(i, i + 1)}'"); + } +} + +// Int and double are the two supported number formats. +example11() { + var i = 1 + 320, d = 3.2 + 0.01; + print("Example11 int ${i}"); + print("Example11 double ${d}"); +} + +// DateTime provides date/time arithmetic. +example12() { + var now = new DateTime.now(); + print("Example12 now '${now}'"); + now = now.add(new Duration(days: 1)); + print("Example12 tomorrow '${now}'"); +} + +// Regular expressions are supported. +example13() { + var s1 = "some string", s2 = "some", re = new RegExp("^s.+?g\$"); + match(s) { + if (re.hasMatch(s)) { + print("Example13 regexp matches '${s}'"); + } else { + print("Example13 regexp doesn't match '${s}'"); + } + } + match(s1); + match(s2); +} + +// Boolean expressions need to resolve to either true or false, as no +// implicit conversions are supported. +example14() { + var v = true; + if (v) { + print("Example14 value is true"); + } + v = null; + try { + if (v) { + // Never runs + } else { + // Never runs + } + } catch (e) { + print("Example14 null value causes an exception: '${e}'"); + } +} + +// 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: '${e}'"); + throw e; // Re-throw + } + } catch (e) { + print("Example15 catch exception being re-thrown: '${e}'"); + } finally { + print("Example15 Still run finally"); + } +} + +// 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); } + print("Example16 dynamic string created with " + "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. +example17() { + print("Example17 " + "concatenate " + "strings " + "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. +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. +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. +example20() { + var s1 = "'\${s}'", s2 = "'\$s'"; + print("Example20 \$ interpolation ${s1} or $s2 works."); +} + +// Optional types allow for the annotation of APIs and come to the aid of +// IDEs so the IDEs can better refactor, auto-complete and check for +// errors. So far we haven't declared any types and the programs have +// worked just fine. In fact, types are disregarded during runtime. +// Types can even be wrong and the program will still be given the +// benefit of the doubt and be run as though the types didn't matter. +// There's a runtime parameter that checks for type errors which is +// the checked mode, which is said to be useful during development time, +// but which is also slower because of the extra checking and is thus +// avoided during deployment runtime. +class Example21 { + List<String> _names; + Example21() { + _names = ["a", "b"]; + } + List<String> get names => _names; + set names(List<String> list) { + _names = list; + } + int get length => _names.length; + void add(String name) { + _names.add(name); + } +} +void example21() { + Example21 o = new Example21(); + o.add("c"); + print("Example21 names '${o.names}' and length '${o.length}'"); + o.names = ["d", "e"]; + print("Example21 names '${o.names}' and length '${o.length}'"); +} + +// Class inheritance takes the form of class name extends AnotherClassName {}. +class Example22A { + var _name = "Some Name!"; + get name => _name; +} +class Example22B extends Example22A {} +example22() { + var o = new Example22B(); + print("Example22 class inheritance '${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 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); + 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. +class Example24A { + var _value; + Example24A({value: "someValue"}) { + _value = value; + } + get value => _value; +} +class Example24B extends Example24A { + Example24B({value: "someOtherValue"}) : super(value: value); +} +example24() { + 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. +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}'"); +} + +// 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 '${_email}'"); + setConfig2("Mary", "Jane"); + print("Example26 name '${_name}', surname '${_surname}', " + "email '${_email}'"); +} + +// Variables declared with final can only be set once. +// In case of classes, final instance variables can be set via constant +// constructor parameter. +class Example27 { + final color1, color2; + // 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 '${o.color2}'"); +} + +// To import a library, use import "libraryPath" or if it's a core library, +// import "dart:libraryName". There's also the "pub" package management with +// its own convention of import "package:packageName". +// See import "dart:collection"; at the top. Imports must come before +// other code declarations. IterableBase comes from dart:collection. +class Example28 extends IterableBase { + var names; + Example28() { + names = ["a", "b"]; + } + get iterator => names.iterator; +} +example28() { + var o = new Example28(); + o.forEach((name) => print("Example28 '${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 +example29() { + var v = true ? 30 : 60; + switch (v) { + case 30: + print("Example29 switch statement"); + break; + } + if (v < 30) { + } else if (v > 30) { + } else { + print("Example29 if-else statement"); + } + callItForMe(fn()) { + return fn(); + } + rand() { + v = new DM.Random().nextInt(50); + return v; + } + while (true) { + print("Example29 callItForMe(rand) '${callItForMe(rand)}'"); + if (v != 30) { + break; + } else { + continue; + } + // 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. +example30() { + var gn, tooHigh = false, + n, n2 = (2.0).toInt(), top = int.parse("123") ~/ n2, bottom = 0; + top = top ~/ 6; + gn = new DM.Random().nextInt(top + 1); // +1 because nextInt top is exclusive + print("Example30 Guess a number between 0 and ${top}"); + guessNumber(i) { + if (n == gn) { + print("Example30 Guessed right! The number is ${gn}"); + } else { + tooHigh = n > gn; + print("Example30 Number ${n} is too " + "${tooHigh ? 'high' : 'low'}. Try again"); + } + return n == gn; + } + n = (top - bottom) ~/ 2; + while (!guessNumber(n)) { + if (tooHigh) { + top = n - 1; + } else { + bottom = n + 1; + } + n = bottom + ((top - bottom) ~/ 2); + } +} + +// 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()); +} + +``` + +## Further Reading + +Dart has a comprehenshive web-site. It covers API reference, tutorials, articles and more, including a +useful Try Dart online. +http://www.dartlang.org/ +http://try.dartlang.org/ + + + |