MESSAGE
| DATE | 2011-04-11 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] C++ Workshop templated operator()<<]
|
as I understand things, the operator<<() needs to be external as to the
class and then declared as a friend of the class. I'm not sure if I
understand why that is the case.
I did this with a class called MESSAGE and had not trouble with the
general implementation. However, when I tried to do this with a
templated class that generally looks like, although this is not compiling
namespace stats{
template
class Distribution {
template friend std::ostream & operator<<(std::ostream &, const
Distribution&);
public:
/* ==================== LIFECYCLE ======================================= */
Distribution (T descr, int occurances = 0);
Distribution():freq(NULL),occurances(NULL){};
// Distribution ( const Distribution &other ); /* copy constructor */
// ~Distribution (); /* destructor */
/* ==================== ACCESSORS ======================================= */
T description(){ return freq;}
int population() { return occurances; }
/* ==================== MUTATORS ======================================= */
void increase_occ(){ ++occurances; std::cout << "description " << freq
<< " occurances " << occurances << std::endl; }
void descrease_occ(){ --occurances; }
/* ==================== OPERATORS ======================================= */
//Distribution& operator = ( const Distribution &other ); /* assignment
operator */
int operator()(){
return freq;
}
bool operator==(Distribution &tmp){
if(this->freq == tmp.freq)
return true;
return false;
}
bool operator<(Distribution &tmp){
if(freq < tmp.freq)
return true;
return false;
}
protected:
/* ==================== DATA MEMBERS
======================================= */
private:
/* ==================== DATA MEMBERS
======================================= */
T freq; //description of how many times found in a List
int occurances; //description of how many times a frequency was found in
a list
}; /* ----- end of class Distribution ----- */
template
std::ostream & operator << ( std::ostream & os, const Distribution &
obj )
{
T desc = obj.description();
int pop = obj.population();
os << "The Identification of " << desc << " was seens " << pop ;
return os;
} /* ----- end of function operator << ----- */
Not this is not compiling because:
test_del.cpp|90| error: passing ?const stats::Distribution? as
?this? argument of ?T stats::Distribution::description() [with T =
int]? discards qualifiers
which is on the call for the use of the << operator on the class. before
I templated
the operaotr<<(), I got a warning that I was using a non-templated
function. I've done some research and this
peoblem seems to have been common, but I don't know of any solutions,
and I don't understand what the implementation
issue is.
----- End forwarded message -----
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