Re: Figure out why member function pointer doesn't work?

SG <>
Tue, 5 Apr 2011 00:22:47 -0700 (PDT)
On 5 Apr., 03:41, Nephi Immortal wrote:

Operator->* and operator-> are very similar. Why can't I use
operator->* to call struct data's member function to pointer?

First of all, you need to recognize that the precedence of operator->
is higher than of the operator->*:

  x->y->z is grouped like this: (x->y)->z


  x->*y->z is grouped like this: x->*(y->z)

Secondly, what you are trying to do cannot work without a proxy
callable object. In order to make


work your operator->* function would need to return something that is
callable. Unfortunately, the result of ptr->*pmemfun where ptr is a
raw pointer and pmemfun is a member function pointer can only be used
as operand for the function call operator. You cannot return the
result of ptr->*pmemfun from a function and delay the function call
this way. C++ does not allow this.

If you want to support operator->* to be able to invoke member
functions you could try somehting like this:

  struct bound_data_memfun {
    data* ptr;
    pGo pmemfun;
    void operator()() const {return (ptr->*pmemfun)();}
    // ^^^^^^^^^^^^^
    // can only be used in combinaton with the function call
    // operator.

  struct storage {
    bound_data_memfun operator->*(pGo pmemfun)
      bound_data_memfun result = {pData,pmemfun};
      return result;

IMHO it's not worth the hassle, though. None of the popular smart
pointer classes overload the operator->* and there is no harm in that.
Simply write


and be done.


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