MESSAGE
| DATE | 2011-05-24 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] template implicit converstion
|
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Xref: panix comp.lang.c++:1085272
> I'm having trouble understanding why my program is making a change in the
> argument type of my template class function
A short answer is that what you are seeing is due to an implicit
conversion that is part of the C++ programming language. If you do
not want this implicit conversion done, declare the constructor
being used by the implicit conversion as explcit, as it
class Distribution {
public:
explicit Distribution(int i) {
// whatever the constructor does
}
}
What follows are details, with most of the source you gave snipped
down to essentials.
> template < class T >
> void List::find_value(T val)
> {
[snip]
> }
[snip]
> 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){
[snip]
> chainlist::List > * dump;
> dump->find_value(search_val);
[snip]
> }
[snip]
The expression
stats::mean_list(tallies, 7 )
implicitly instantiates the mean_list function template. Due to the
argument types, the instantiated function includes the declaration
chainlist::List > * dump;
The expression
dump->find_value(search_val)
implicitly instantiates the find_value member function template.
Due to the type of the object for which the member function is
called, the instantiated member function is
void List >::find_value(
stats::Distribution val)
In the call to that function by dump->find_value(search_val), an
implicit conversion by constructor is done to convert the search_val
argument (of type int) to a stats::Distribution (the type of
the parameter).
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