I am trying to inherit a parent method to child method. In the following inheritance, I am not able to call the "super" method for getting the getName() method inside child class. I can't understand what is the problem. Hopes someone can help me on this. Code is as follows. Thanks in Advance!
class Parent{
constructor(name){
this.name=name;
this.getName=function(){
console.log(this.name);
}
}}
class Child extends Parent {
constructor(name,age){
super(name)
this.age=age;
this.getNameAndAge=function(){
super.getName(); // this line is the error
console.log(this.age);
}
}}
let one=new Parent("Shaju");
one.getName();
let two=new Child("Sibu",49);
two.getNameAndAge();
Related
I'm defining some custom Exceptions in Dart.
I want in my logic to check the type of exception and base my processing on that, so I want to create distinct classes for each, for example like this :
class FailedToLoadCriticalDataException implements Exception { } // app cannot continue
class FailedToLoadNonCriticalDataException implements Exception { } // app can continue
However I also want to pass 2 parameters when I create these types of exceptions, the type of API call, and the API url, and the definition for that would look like this :
class UrlCallFailedException implements Exception {
String _dataTypeName;
String _urlEndpoint;
UrlCallFailedException([this._dataTypeName, this._urlEndpoint]);
#override
String toString() {
return "(${this.runtimeType.toString()}) Failed to fetch $_dataTypeName ($_urlEndpoint)";
}
}
Now what I want to do is (replace the initial definitions I made earlier and re)define my FailedToLoadCriticalDataException and FailedToLoadNonCriticalDataException classes so that they are exactly the code that is in the UrlCallFailedException class.
Is there any way to simply say something like class FailedToLoadCriticalDataException **is** UrlCallFailedException; and not need to duplicate the code that defines UrlCallFailedException ?
class FailedToLoadCriticalDataException implements UrlCallFailedException{ } is wrong because it is "Missing concrete implementations of 'getter UrlCallFailedException._dataTypeName',.."
class FailedToLoadCriticalDataException extends UrlCallFailedException{ } is wrong because when I got to throw FailedToLoadNonCriticalDataException("Foo", url); it's expectation is that there are no params ("Too many positional arguments: 0 expected, but 2 found.").
Is there a way to create multiple classes that behave exactly the same as another type and differ only in their class, without duplicating all the code ?
I've come up with this as a decent compromise :
class FailedToLoadCriticalDataException extends UrlCallFailedException {
FailedToLoadCriticalDataException([dataTypeName, urlEndpoint]) {
super._dataTypeName = dataTypeName;
super._urlEndpoint = urlEndpoint;
}
}
class FailedToLoadNonCriticalDataException extends UrlCallFailedException {
FailedToLoadNonCriticalDataException([dataTypeName, urlEndpoint]) {
super._dataTypeName = dataTypeName;
super._urlEndpoint = urlEndpoint;
}
}
Some, but minimal, code duplication, and I can now call throw FailedToLoadNonCriticalDataException("Foo", url); in my code later.
I need some help to understand everything correctly.
I want to check a pointer to a abstract class if it is instance of a specific child class.
I have one abstract class "kunde" and two child classes "firmenkunde" and "privatkunde" who inherit the methods of kunde.
In order to search by "int knr" (int customer number) I use as return type a pointer to "kunde".
Within the database class I get back the "kdstatus" and use
kunde * kd = new privatkunde(0);
if the status is PK or new firmenkunde(0) if it would be FK.
The abstract class kunde doesn't have any attribute I could use to save the status.
This way I did hope to be able to ask, if the returned pointer would be an instance of the class privatkunde or firmenkunde. But I did not found any method to do this.
MessageBox::Show(marshal_as<String^>(typeid(kd).name()));
I did ask the typeid name but this only returns "class kunde *" and is not what I want to know.
Is there a way to work around this problem?
You can use typeid as you mentioned. Using the polymorphism, you can write:
kunde * kd = new privatkunde(0);
if(typeid(kd) == typeid(privatkunde))
{
// This is a privatkunde objet
}
See here to have more explanation.
The problem you encounter is that your kunde class is not polymorphic. As commented by #George, see how the virtual methods work.
I hope it can help.
Generally you can use dynamic_cast for this.
An example:
class Parent
{
public:
virtual ~Parent();
virtual void do_thing()= 0;
};
class Child1: public Parent
{
public:
void do_thing() override
{
//...
}
};
class Child2: public Parent
{
public:
void do_thing() override
{
//...
}
};
void use_parent(Parent* p)
{
auto c1_ptr = dynamic_cast<Child1*>(p);
if(c1_ptr != nullptr)
{
// p is a Child1
do_thing_with_child1(c1_ptr);
}
auto c2_ptr = dynamic_cast<Child2*>(p);
if(c2_ptr != nullptr)
{
// p is a Child2
do_thing_with_child2(c2_ptr);
}
}
While this works, it becomes difficult to maintain if you have multiple child classes. You have to remember to add a case for each new child class you define.
A better way to structure something like this would be to use the "Tell, don't ask" concept when designing your object-oriented systems. A great write-up on this concept can be found here.
Is it possible to write a normal function in the controller?
I want to clean up my code a bit, so I want to write some methods for repeated code segments, but I don't want to create a special class.
How is it possible to do this?
If I do a normal
private function xyz () {}
I got a function not found error.
You should use protected, not private unless you have very good reasons to do so. Anyway, defining additional methods work fine for me.
You need to call this method with $this->xyz().
A good solution might be using an abstract class if you want to share methods accross controllers:
abstract class AbstractController extends \TYPO3\CMS\Extbase\Mvc\Controller\ActionController{
protected function myFunction(){}
}
Your controllers inherit from the abstract class and will have all methods available:
class FirstController extends AbstractController {
public function firstAction(){
// has access to myFunction()
}
}
class SecondController extends AbstractController {
public function secondAction(){
// has access to myFunction()
}
}
How do I create a template that each time when I create a class that extends MyClass, it will automatically add 3 functions.
EDIT:
In other words I am trying to implement Abstract functionality in AS3. Assume that MyClass have both private and protected methods.
I see the only way to write own code template and call it every time you need, in Flash Builder: window->preference->flash builder->editors->code template->action script->new and give the name to the template, for instance myclass.
You can use existed templates as an example for template syntax.
Template code for MyClass child class with three methods:
import my.package.MyClass
/**
* #author ${user}
*/
public class ${enclosing_type} extends MyClass
{
public function ${enclosing_type}()
{
}
override public function publicMethod():void
{
}
override protected function protectedMethod():void
{
}
override private function privateMethod():void
{
}
${cursor}
}
Usage:
Create new "action script file" or "new class",
remove all file content
type myclass and choose from auto-complete options template myclass
If you are actually extending MyClass, all of MyClass's functions are already available to your descendants. You can also override either of them with old header and desired new body, and still be able to call older versions of those functions via super qualifier. So, you add those functions to MyClass and let them be.
Another way is to make an interface - it's a set of declarations without any function bodies, which you have to implement in any class that wants this interface in its content. A short introduction to interfaces. Then your MyClass will be an interface, with 3 function declarations in it, and whichever class will be declared as implements MyClass will have to provide bodies for these functions.
Check other keywords on that page, including extends and implements.
Hope this helps.
EDIT: There are no abstract classes in AS3, however you can emulate abstract functions in a normal class via exception throwing:
protected function abstractFunction(...params):void {
throw new Error("Abstract!");
}
inside of my Zend_Db_Table_Rowset Object i found this:
["_primary:protected"]
... does anybody if theres a way to access this? ... maybe something like
$rowsetObject->getPrimary()
Thanks for your help,
Alex
Zend_Db_Table_Rowset has no property _primary. What you are refering to is either the Zend_Db_Table instance you got the Rowset from or a Zend_Db_Table_Row instance inside the Rowset.
For getting the primary key from a Zend_Db_Table instance you can do:
$tableInstance->info('primary')
For getting the primary key from a Zend_Db_Table_Row instance you can get the table instance and call info() on it:
$rowInstance->getTable()->info('primary')
Note that this will not work when the row is disconnected, because then getTable() will return null.
Or, when using a custom Zend_Db_Table_Row you can add a method that proxies to _getPrimaryKey():
class My_Db_Table_Row extends Zend_Db_Table_Row
{
public function getPrimaryKey()
{
return $this->_getPrimaryKey();
}
}
Since this variable is protected, you can extend Zend_Db_Table_Rowset and define getPrimary() function yourself, e.g.
class My_Zend_Db_Table_Rowset extends Zend_Db_Table_Rowset {
//put your code here
function getPrimary() {
return $this->_primary;
}
}