MESSAGE
| DATE | 2011-05-23 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] Template Argument type deterination
|
I'm having trouble understanding why my program is making a change in
the
argument type of my template class function
template < class T >
void List::find_value(T val)
{
cursor() = front();
while(cursor() != endd()){
if (*(cursor()->value()) == val)
return;
else{
cursor(cursor()->next());
}
}
if(*(endd()->value()) == val)
return;
else{
cursor() = 0; //park the cursor when nothing is found
}
}
It's part of a List template class
I call it from a templated fucntion in a different namespace as follows:
tally = new chainlist::List >;
tallies = new chainlist::List< chainlist::List< stats::Distribution
> *>;
std::cout << "The standard mean for picking 7 is ==> " <<
stats::mean_list(tallies, 7 ) << std::endl;;
template
float mean_list(chainlist::List<
chainlist::List >* > * tallies, T search_val){
if(tallies->endd() == 0){
std::cout << "Empty List" << std::endl;
return 0.0;
}
int sum = 0;
chainlist::List > * dump;
tallies->cursor() = tallies->front();
while(tallies->cursor() != tallies->endd() ){
//tallies->cursor()->value()->find_value(search_val);
dump = *(tallies->cursor()->value());
//dump->cursor() = dump->endd();
//std::cout << "Testing\n" <<
//*(dump->cursor()->value()) << std::endl;
dump->find_value(search_val);
if(dump->cursor() != NULL)
sum += dump->cursor()->value()->population();
tallies->cursor(tallies->cursor()->next());
}
dump = *(tallies->cursor()->value());
dump->find_value(search_val);
if(dump->cursor() != 0)
sum += dump->cursor()->value()->population();
float tot = (float) sum/(float)(tallies->size());
std::cout << "Mean " << tot << " sum " << sum << " size " <<
tallies->size() << std::endl;
return tot;
}
Now T is an integer for mean_list, and the first argument is of type
chainlist::List< chainlist::List >* > * when
called and the second argument is of type int
I then pass int search_val to method chainlist::List::find_value(T)
where T = stats::Distribution (where T is an int)
on this line:
dump->find_value(search_val);
and that's where the weirdness happens. I have a type mismatch since
I'm sending by value an integer instead of a stats::Distribution
Instead the program calls the stat::Distribution constructor using 7,
the value of search_val, as an argument redrawing search_val as type
to a Distribution
:in gdb
312 void List::find_value(T val)
313 {
314 cursor() = front();
315 while(cursor() != endd()){
316 if (*(cursor()->value()) == val)
317 return;
318 else{
319 cursor(cursor()->next());
320 }
321 }
322 if(*(endd()->value()) == val)
323 return;
324 else{
325 cursor() = 0; //park the cursor when nothing is found
326 }
327 }
chainlist::List >::find_value (this=0x804f008,
val=...) at linklist.h:314
(gdb) ptype val
type = class stats::Distribution {
public:
chainlist::List > *tally;
private:
int freq;
int occurances;
public:
void Distribution(int, int);
void Distribution(void);
int description(void) const;
int population(void) const;
void increase_occ(void);
void descrease_occ(void);
int operator()(void);
bool operator==(stats::Distribution &);
bool operator<(stats::Distribution &);
float stddev(chainlist::List > *);
}
What rule for Template argument matching allows for this kind of magic?
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