Justine Jose

• Jun 29th, 2015

 

When a function is declared virtual, it tells the compiler that the type of object which invoked this function should be declared at the run time, and invoke the appropriate function based on the type of object.
Similarly, when a constructor is declared virtual, it tells the compiler that the type of object which invoke this constructor should be declared at the run time. But for creating an object, the exact type of object should be known at compile time rather than at run time. Thats why constructors are not virtual.

Aarish

• Apr 20th, 2016

 

Advanced C++ | Virtual Constructor
Can we make a class constructor virtual in C++ to create polymorphic objects? No. C++ being static typed (the purpose of RTTI is different) language, it is meaningless to the C++ compiler to create an object polymorphically. The compiler must be aware of the class type to create the object. In other words, what type of object to be created is a compile time decision from C++ compiler perspective. If we make constructor virtual, compiler flags an error. In fact except inline, no other keyword is allowed in the declaration of constructor.
In practical scenarios we would need to create a derived class object in a class hierarchy based on some input. Putting in other words, object creation and object type are tightly coupled which forces modifications to extended. The objective of virtual constructor is to decouple object creation from it’s type.

James Thompson

• Aug 23rd, 2016

 

Because the virtual pointer table isnt initialised till after the constructor is complete.