c++ - Overloading operator+ with pointers -

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i'm working on project on polymorphism in c++ , have lots of pointers. need overload operator +, can write following expression naturally:

c=a+b;

with a,b , c being declared as:

a *a,*b,*c;

the basic overloading definitions know are

a &operator+(const a& a) &operator=(const a& a)

but following errors:

invalid initialization of non-const reference of type 'a&' rvalue of type 'a* const' invalid operands of types 'a*' , 'a*' binary 'operator+'

how should write overloaded operator can call naturally?

i know following suggestion not want, sake of completeness tried find solution template wrapper class around pointers would permit overloading operator+. wondered combination of lookup rules, template arguments , type conversion achieve. turns out "natural" use of operator+ seems impossible, explicit call works. here code:

/** wrapper class around arbitrary pointer types */ template<class tptr> class myptrt {     public:     tptr ptr;     myptrt(const tptr p = 0) :ptr(p)         {} };  /** plus operator on myptrts */ template<class t>  const myptrt<t>&  operator+(const myptrt<t> &l, const myptrt<t> &r)  {      return l;  }  myptrt<int *> mp1, mp2, mp3; int *ip;

ok, works these declarations?

// works (template type explicit) ... mp3 = operator+<int *>(ip, ip);  // ... , works (of course, // arguments match template declaration) ... mp3 = mp1 + mp2;

and doesn't (with gcc 4.8.3)?

mp3 = mp1 + ip;

the error is:

smartpointplus.cpp:33:12: error: no match ‘operator+’ (operand types ‘myptrt<int*>’ , ‘int*’)   mp3 = mp1 + ip;             ^ smartpointplus.cpp:33:12: note: candidate is: smartpointplus.cpp:13:1: note: template<class t> const myptrt<t>& operator+(const myptrt<t>&, const myptrt<t>&)  operator+(const myptrt<t> &l, const myptrt<t> &r)  ^ smartpointplus.cpp:13:1: note:   template argument deduction/substitution failed: smartpointplus.cpp:33:14: note:   mismatched types ‘const myptrt<t>’ , ‘int*’

i'm not quite sure why compiler doesn't construct myptrt int* argument. see proper function. perhaps wrong ctor?

mp3 = operator+(ip, ip);

the error message similar. template function considered compiler cannot convert arguments.

smartpointplus.cpp:36:24: error: no matching function call ‘operator+(int*&, int*&)’   mp3 = operator+(ip, ip);                         ^ smartpointplus.cpp:36:24: note: candidate is: smartpointplus.cpp:13:1: note: template<class t> const myptrt<t>& operator+(const myptrt<t>&, const myptrt<t>&)  operator+(const myptrt<t> &l, const myptrt<t> &r)  ^ smartpointplus.cpp:13:1: note:   template argument deduction/substitution failed: smartpointplus.cpp:36:24: note:   mismatched types ‘const myptrt<t>’ , ‘int*’   mp3 = operator+(ip, ip);

it's bit sad operator+(ip, ip) (automatically trying deduce template type) doesn't work. limits usability ;-). 1 have templatize functions using operator in order avoid providing template type explicitly every call. infix notation below, contrast, doesn't consider template operator:

mp3 = ip + ip;

the error message short:

smartpointplus.cpp:38:13: error: invalid operands of types ‘int*’ , ‘int*’ binary ‘operator+’   mp3 = ip + ip;

i thought infix , function style notation of operator calls just, well, notational differences, apparently change lookup rules.

tl;dr: op wanted (an infix plus operation pointer arguments) doesn't work template wrapping class, afaict.


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