Efficient C++ Performance Programming Techniques

Inlining Virtual Methods

We previously noted that some compilers will refuse to inline virtual methods. This may have seemed like it should be obvious. After all, a virtual method is one for which the binding is delayed until run-time. Virtual methods are generally considered to be always called indirectly via a function pointer table. Although this view of virtual methods is in general accurate, it is not totally so. Take, for example, the following code fragment:

inline
virtual
int x::y (char* a)
{
    ...
}

void z (char* b)
{
    x_base* x_pointer = new x(some_arguments_maybe);
    x x_instance(maybe_some_more_arguments);
    x_pointer->y(b);
    x_instance.y(b);
}

y() is a virtual method, but its binding doesn't always need to be delayed until runtime. In ...