MESSAGE
| DATE | 2011-05-24 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] [billy.donahue@gmail.com: Re: [mrbrklyn@panix.com: Template
|
----- Forwarded message from Billy -----
Date: Tue, 24 May 2011 12:25:09 -0400
From: Billy
To: Ruben Safir
Subject: Re: [mrbrklyn-at-panix.com: Template Argument type deterination]
You didn't provide the constructor of stats::Distribution. If a constructor
takes a single argument, it will be considered a conversion operator unless
it is marked 'explicit'. Most style guides including Google's urge
programmers to mark any single argument constructor as 'explicit', which
make it ineligible as a conversion operator.
Another thing is that maybe an integer is being used as a pointer or
something.
I can't really tell exactly through the levels of indirection.
I'm uneasy because I don't see a single-arg constructor in the 'gdb' ptype
output.
But that isn't source code, that's gdb output. Only source code matters.
The constructor might have been inlined and optimized away, for example.
On Mon, May 23, 2011 at 4:50 PM, Ruben Safir wrote:
> ----- Forwarded message from Ruben Safir -----
>
> Date: Mon, 23 May 2011 16:35:54 -0400
> From: Ruben Safir
> To: hangout-at-nylxs.com
> Subject: Template Argument type deterination
> User-Agent: Mutt/1.5.20 (2009-06-14)
>
>
> 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?
>
>
> ----- End forwarded message -----
>
> --
> http://www.mrbrklyn.com - Interesting Stuff
> http://www.nylxs.com - Leadership Development in Free Software
>
> So many immigrant groups have swept through our town that Brooklyn, like
> Atlantis, reaches mythological proportions in the mind of the world - RI
> Safir 1998
>
> http://fairuse.nylxs.com DRM is THEFT - We are the STAKEHOLDERS - RI
> Safir 2002
>
> "Yeah - I write Free Software...so SUE ME"
>
> "The tremendous problem we face is that we are becoming sharecroppers to
> our own cultural heritage -- we need the ability to participate in our own
> society."
>
> "> I'm an engineer. I choose the best tool for the job, politics be
> damned.<
> You must be a stupid engineer then, because politcs and technology have
> been attached at the hip since the 1st dynasty in Ancient Egypt. I guess
> you missed that one."
>
> ? Copyright for the Digital Millennium
>
--
?n??uop ?ll?q
----- End forwarded message -----
|
|
