Type Casting for User Defined Objects

Type casting for user defined objects

There is no need to type cast in php.

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Edit: Since this topic seems to cause some confusion, I thought I'd elaborate a little.

In languages such as Java, there are two things that may carry type. The compiler has a notion about type, and the run time has another idea about types. The compilers types are tied to variables, whereas the run time engine tracks the type of values (Which are assigned to variables). The variable types are known at compile time, whereas the value types are only known at run time.

If a piece of input code violates the compilers type system, the compiler will barf and halt compilation. In other words, it's impossible to compile a piece of code that violates the static type system. This catches a certain class of errors. For example, take the following piece of (simplified) Java code:

class Alpha {}

class Beta extends Alpha {
  public void sayHello() {
    System.out.println("Hello");
  }
}

If we now did this:

Alpha a = new Beta();

we would be fine, since Beta is a subclass of Alpha, and therefore a valid value for the variable a of type Alpha. However, if we proceed to do:

a.sayHello();

The compiler would give an error, since the method sayHello isn't a valid method for Alpha - Regardless that we know that a is actually a Beta.

Enter type casting:

((Beta) a).sayHello();

Here we tell the compiler that the variable a should - in this case - be treated as a Beta. This is known as type casting. This loophole is very useful, because it allows polymorphism in the language, but obviously it is also a back door for all sorts of violations of the type system. In order to maintain some type safety, there are therefore some restrictions; You can only cast to types that are related. Eg. up or down a hierarchy. In other words, you wouldn't be able to cast to a completely unrelated class Charlie.

It's important to note that all this happens in the compiler - That is, it happens before the code even runs. Java can still get in to run time type errors. For example, if you did this:

class Alpha {}

class Beta extends Alpha {
  public void sayHello() {
    System.out.println("Hello");
  }
}

class Charlie extends Alpha {}

Alpha a = new Charlie();
((Beta) a).sayHello();

The above code is valid for the compiler, but at run time, you'll get an exception, since the cast from Beta to Charlie is incompatible.

Meanwhile, back at the PHP-farm.

The following is valid to the PHP-compiler - It'll happily turn this into executable byte code, but you'll get a run time error:

class Alpha {}

class Beta extends Alpha {
  function sayHello() {
    print "Hello";
  }
}
$a = new Alpha();
$a->sayHello();

This is because PHP variables don't have type. The compiler has no idea about what run time types are valid for a variable, so it doesn't try to enforce it. You don't specify the type explicitly as in Java either. There are type hints, yes, but these are simply run time contracts. The following is still valid:

// reuse the classes from above
function tellToSayHello(Alpha $a) {
  $a->sayHello();
}
tellToSayHello(new Beta());

Even though PHP variables don't have types, the values still do. A particular interesting aspect of PHP, is that it is possible to change the type of a value. For example:

// The variable $foo holds a value with the type of string
$foo = "42";
echo gettype($foo); // Yields "string"
// Here we change the type from string -> integer
settype($foo, "integer");
echo gettype($foo); // Yields "integer"

This feature some times confused with type casting, but that is a misnomer. The type is still a property of the value, and the type-change happens in runtime - not at compile time.

The ability to change type is also quite limited in PHP. It is only possible to change type between simple types - not objects. Thus, it isn't possible to change the type from one class to another. You can create a new object and copy the state, but changing the type isn't possible. PHP is a bit of an outsider in this respect; Other similar languages treat classes as a much more dynamic concept than PHP does.

Another similar feature of PHP is that you can clone a value as a new type, like this:

// The variable $foo holds a value with the type of string
$foo = "42";
echo gettype($foo); // Yields "string"
// Here we change the type from string -> integer
$bar = (integer) $foo;
echo gettype($bar); // Yields "integer"

Syntactically this looks a lot like how a typecast is written in statically typed languages. It's therefore also often confused with type casting, even though it is still a runtime type-conversion.

To summarise: Type casting is an operation that changes the type of a variable (not the value). Since variables are without type in PHP, it is not only impossible to do, but a nonsensical thing to ask in the first place.

How to make type cast for python custom class

As noted by Anand in comments, what you're looking for is object serialization and deserialization. One way to achieve this is through the pickle (or cPickle) module:

>>> import pickle

>>> class Example():
...     def __init__(self, x):
...             self.x = x
...
>>> a = Example('foo')
>>> astr = pickle.dumps(a) # (i__main__\nExample\np0\n(dp1\nS'x'\np2\nS'foo'\np3\nsb.
>>> b = pickle.loads(astr)
>>> b
<__main__.Example instance at 0x101c89ea8>
>>> b.x
'foo'

Note, however, that one gotcha in using the pickle module is dealing with implementation versions. As suggested in the Python docs, if you want an unpickled instance to automatically handle implementation versioning, you may want to add a version instance attribute and add a custom __setstate__ implementation: https://docs.python.org/2/library/pickle.html#object.setstate. Otherwise, the version of the object at serialization time will be exactly what you get at deserialization time, regardless of code changes made to the object itself.

casting object with user defined type

int variable_one=(int)variable_name; is a C style cast.

C++ offers many casting operators:

• dynamic_cast <new_type> (expression)
• reinterpret_cast <new_type> (expression)
• static_cast <new_type> (expression)
• const_cast <new_type> (expression)

Have a look at article about type casting or refer to any C++ introductory book.

User defined Data type to JSON Object type casting using jason.simple

For that use a small trick, Override toString() method in your Object class (here User) like

public class User {

    String id;
    int value;
    String Anime;

    .
    .
    .
    //Getter Setter 
    .
    .
    .

    @Override
    public String toString() {
        return "{" +
            "id=" + id + "," +
            "value=" + value + ","+
            "Anime='" + Anime +
            "}";
    }

}

Type casting user defined object in PHP for Netbeans auto completion

You need to start commenting your code using PHPDoc type comments, Netbeans will use them for auto completion.

protected function _read_excel(PHPExcel $excel)
{
    $sheet = $excel->getSheet(0);   // Works perfectly fine here because I type cast the argument
    $rows = $sheet->getRowIterator(); // Works fine here too
    foreach($rows as $row) 
    {
        /**
         * @var PHPExcel_Worksheet_CellIterator $cols
         */
        $cols = $row->getCellIterator(); // Now netbeans will know what class it is.
    }
}

If you prefer, you can use 'inline' docblocks too :-

/** @var PHPExcel_Worksheet_CellIterator $cols */

Or, in the latest version of NetBeans, the order appears reversed and has one fewer *

/* @var $cold PHPExcel_Worksheet_CellIterator */

However you must make sure that netbeans knows where to find PHPExcel. My answer here gives some guidance on that if you need it.

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