Can't for the life of me understand why this fails:
#include <vector>
#include "boost/algorithm/string/predicate.hpp"
struct Test
:
public std::vector<int>
{
Test() { }
Test(const Test&) { assert(false); }
};
int main()
{
Test a;
Test b;
boost::algorithm::equals(a, b);
return 0;
}
Output:
$ g++ boostEqualsCopyDemo.cpp -I /usr/include/boost-1_47
$ a.out
a.out: boostEqualsCopyDemo.cpp:10: Test::Test(const Test&): Assertion `false' failed.
Aborted (core dumped)
I've tried digging through the boost code but it's making my head spin. It seems absurd; so wasteful and unnecessary. What's going on?
Boost.Range is a collection of concepts and utilities that are particularly useful for specifying and implementing generic algorithms.
You can think of a range as two iterators that refer to the beginning and end of a group of elements that you can iterate over. Because all containers support iterators, every container can be thought of as a range. Since all algorithms from Boost.
Boost is trying to manufacture a set of ranges for the containers you pass in, and it ends up calling range_detail::is_char_ptr()
, which is the name of a set of function templates that uses template parameter deduction to determine if the parameter is a char
pointer of some sort or not (as you might guess by the name).
Unfortunately, the 'catch-all' function template that returns 0
when matching non-char-pointer parameters takes its parameter by value.
I think this can be fixed by changing the parameter to take a const&
instead. Look in the file boost/range/as_literal.hpp
for:
template< class T >
inline long is_char_ptr( T /* r */ )
{
return 0L;
}
and change it to:
template< class T >
inline long is_char_ptr( T const& /* r */ ) // <-- add const&
{
return 0L;
}
I'm by no means an expert in the implementation of complex template libraries (I use 'em, I don't write 'em), so I make no claims that this change won't cause some other nasty side-effect.
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