Generics in Dart: <> merkkien käyttöä, T, E , DART:issa

This article is fully to be modified

Lisäksi DART kielessä on näitä <T>   <E>  ilmaisuja.  Muiden sulkumerkkien jälkeen ne pysähdyttävät hieman miettimään...    Miksi juuri  T   ja  E  ?
(K,V)  Tarkoittaa siis Key ja Value,  sehän on selvää.
Kokoan leikkeitä ohjeista:

http://www.dartlang.org/language-tour/#generics

Generics

If you look at the API documentation for the basic array type, List, you'll see that the type is actuallyList<E>. The <...> notation marks List as a generic (or parameterized) type—a type that can declare formal type parameters.
For example, if you intend for a list to contain only strings, you can declare it as List<String> (read that as "List of String").
....
Generic types can save you the trouble of creating all these interfaces. Instead, you can create a single interface that takes a type parameter:
interface Cache<T> {
  T getByKey(String key);
  setByKey(String key, T value);
}
In this code, T is the stand-in type. It's a placeholder that you can think of as a type that a developer will define later.
Using collection literals

Both built-in collection types are parameterized: lists and maps. Parameterized literals are just like the literals you've already seen, except that you add <type> before the opening bracket. For example:
List<String> names = <String>['Seth', 'Kathy', 'Lars'];
Map<String, String> pages = <String>{ // specify value type: String
    'index.html':'Homepage',  // (the key type is implicitly String)
    'robots.txt':'Hints for web robots',
    'humans.txt':'We are people, not machines' };


NO?  Näyttää siltä siis, että <> merkinnän sisällä on "tyyppi"...
..
To specify one or more types when using a constructor, put the types in angle brackets (<...>
..
Generic collections and the types they contain

Dart generic types are reified, which is a fancy way of saying that they carry their type information around at runtime.
= = = = = = = = = = = = = = = = = = = = = = = = =

http://api.dartlang.org/dart_core.html
Collection<E>  
HashSet<E>
Iterable<E>
Iterator<E>
List<E>
Queue<E>
Set<E>


HashMap<K, V>
LinkedHashMap<K, V>
Map<K, V>       mapping a key to a value.


Completer<T>
Future<T>


SIIS:  E   T   K   V
What is this T  in <T>  ?
Interface Future<T>

A Future is used to obtain a value sometime in the future. Receivers of a Future obtain the value by passing a callback to then.

========================================================

What is this   E   in <E>  ?

===========================================

http://www.dartlang.org/language-tour/#Typedefs
Typedefs can be parameterized.
typedef int Compare<T>(T a, T b);

class SortedCollection<T> {
  Compare<T> compare;
  SortedCollection(this.compare);
}

main() {
  SortedCollection<int> s = new SortedCollection<int>((a,b) => a - b);
  print(s.compare is Compare<int>);  // true
  print(s.compare('a','b'));  // checked mode throws exception
}
dartlang  0.08

typeParameter:
identifier (extends type)?
;
typeParameters:
`<' typeParameter (`,' typeParameter)* `>'
;
A type parameter T may be suffixed with an extends clause that specifies
the upper bound for T.

A type parameter T may be suffixed with an extends clause that specifies
the upper bound for T.   ....

Tässäpä hieman sulattelemista...    Täydennän tekstiä vielä...


http://c.dart-examples.com/learn/variables/collections
Tämä kirjoitus tuo hieman lisävalaistusta asiaan...

.published originally in  etdart.blogspot.fi

Overloading, what do'esw it mean? mitä se tarkoittaa, DART ym. kielet

Like most dynamically-typed languages, Dart doesn't support overloading....

http://japhr.blogspot.com/2012/02/overloading-dart-operators-for-great.html
Overloading Dart Operators for Great Evil

http://en.wikipedia.org/wiki/Overloading

Constructor and function/method overloading, in computer science, a type of polymorphism where different functions with the same name are invoked based on the data types of the parameters passed
Operator overloading, a form of functional or method overloading where the action being overloaded is an operator, such as + or -

http://www.parashift.com/c++-faq-lite/operator-overloading.html

It allows you to provide an intuitive interface to users of your class, plus makes it possible for templates to work equally well with classes and built-in/intrinsic types.
Operator overloading allows C/C++ operators to have user-defined meanings on user-defined types (classes). Overloaded operators are syntactic sugar for function calls...



Ja tähän Dart-kielestä esimerkkejä...



Function Overloading - General Dart Discussion | Google Groups
Oct 30, 2011 ... I'm progamming complex object and I am a little dissapointed with some aspect like it haven't got Methods Overloading. I think here could be ...
LabeledDiscussions
Constructor overloading - General Dart Discussion | Google Groups
Feb 12, 2012 ... Subject: Constructor overloading ... Why Dart doesn't allow to overloadconstructors. I have to define ... Subject: Re: Constructor overloading ...
LabeledDiscussions
Operator Overloading: "Convert" Operator - General Dart Discussion ...
Feb 13, 2012 ... I have seen this in other languages as an overloading of the "Convert" operator. Is this possible in Dart? For example: class Material{ ... } ...
LabeledDiscussions

http://www.dartlang.org/articles/idiomatic-dart/

Named constructors

Like most dynamically-typed languages, Dart doesn't support overloading. With methods, this isn't much of a limitation because you can always use a different name, but constructors aren't so lucky. To alleviate that, Dart lets you define named constructors:
class Point {
  num x, y;
  Point(this.x, this.y);
  Point.zero() : x = 0, y = 0;
  Point.polar(num theta, num radius) {
    x = Math.cos(theta) * radius;
    y = Math.sin(theta) * radius;
  }
}
Here our Point class has three constructors, a normal one and two named ones. You can use them like so:
var a = new Point(1, 2);
var b = new Point.zero();
var c = new Point.polar(Math.PI, 4.0);
Note that we're still using new here when we invoke the named constructor. It isn't just a static method.
.     originally published in   etdart.blogspot.fi