From d099e6c7dd0ba09a4a8e43e82045783f356a8234 Mon Sep 17 00:00:00 2001 From: Emiel Bruijntjes Date: Thu, 6 Mar 2014 21:50:14 +0100 Subject: update documentation --- documentation/constructors-and-destructors.html | 90 +++++++------------------ 1 file changed, 26 insertions(+), 64 deletions(-) (limited to 'documentation') diff --git a/documentation/constructors-and-destructors.html b/documentation/constructors-and-destructors.html index 42a6699..8b9211f 100644 --- a/documentation/constructors-and-destructors.html +++ b/documentation/constructors-and-destructors.html @@ -5,59 +5,21 @@

A C++ constructor is called on an object that is being initialized, - but that is not in an initialized state yet. You can experience this by - calling a pure virtual method from a constructor. This will make your - program crash, even when the pure virtual method was implemented in the - derived class. The reason for this is that inside the C++ constructor the - object is not yet fully initialized, and the object is not yet aware of - it's position in the class hierarchy. The call to the pure virtual method - can thus not be passed on to the derived object. + but that is not in an initialized state yet. You can experience + this by calling a virtual method from the constructor. Even when this virtual + method was overridden in a derived class, this will always execute the method + of the class itselves, and not the overridden implementation. The reason + for this is that during the call to the C++ constructor the object is not yet + fully initialized, and the object is not yet aware of it's position in the + class hierarchy. The call to the virtual method can thus not be passed + on to the derived object.

-


-#include <iostream>
-
-// define a base class with a pure virtual method that is called from the
-// constructor
-class BASE 
-{
-public:
-    // constructor
-    BASE() 
-    {
-        // call the pure virtual method
-        doSomething();
-    }
-    
-    // define method that should be implemented by derived classes
-    virtual void doSomething() = 0;
-};
-
-// define a derived class
-class DERIVED : public BASE 
-{
-public:
-    // implementation of the virtual function
-    virtual void doSomething() override 
-    {
-        std::cout << "doSomething()" << std::endl;
-    }
-};
-
-// main procedure
-int main()
-{
-    DERIVED d;
-    return 0;
-}
-
-

-

- The above program crashes (some compilers even refuse to compile this). - In PHP however, when the __construct() method - gets called, the object is already fully initialized and it is perfectly - legal to make calls to abstract methods that are implemented in derived - classes, as you can see in the following example. + In PHP however, the __construct() method has a different behavior. When + it gets called, the object is already fully initialized and it is perfectly + legal to make calls to even abstract methods that are implemented in derived + classes. The following PHP script is completely legal - but it is impossible + to do a similar thing in C++. 


@@ -93,22 +55,22 @@ $d = new DERIVED();

- This PHP script correctly outputs 'doSomething()'. This happens because the - __construct() method in PHP does not really construct anything, it - has access to all members, and (when available) - also the base class and overridden methods. In fact, __construct() is not a - constructor at all, but a very - normal method that just happens to be the first method that is called right - after the object is constructed, and that is called automatically. + This script outputs 'doSomething()'. In fact, __construct() is not a + constructor at all, but a very normal method that just happens to be the + first method that is called, and that is called automatically after the + object is constructed.

This difference is important for you as a C++ programmer, because you should - never confuse your C++ constructor with the __construct() method. In the C++ - constructor, the C++ object is being constructed and the - PHP object does not yet exist. After the constructor is finished, the PHP engine - will create the PHP object, and the PHP-CPP library will link that PHP object - to your C++ class. And only then the __construct() method gets called. It is therefore - valid to have both a C++ constructor and a __construct() method in your class. + never confuse your C++ constructor with the PHP __construct() method. In the C++ + constructor, the object is being constructed and the PHP object does not + yet exist. After the constructor is finished, the PHP engine + takes over control and creates the PHP object, and the PHP-CPP library then + links that PHP object to your C++ object. Only after both the PHP object and + the C++ object are fully constructed, the __construct() method is called - just + like a normal method. It is therefore not uncommon to have both a C++ constructor + and a __construct() method in your class. The C++ constructor to initialize + the member variables, and __construct() to activate the object. 


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