When trying to build some legacy code (with a recent version of boost), I stumbled upon the following problem:
#include <boost/scoped_array.hpp>
bool foo(const boost::scoped_array<int> bar) {
return bar;
}
bool foo2(const boost::scoped_array<int> bar) {
const bool r = bar;
return r;
}
bool foo3(const boost::scoped_array<int> bar) {
return bar ? true : false;
}
The above source will not compile. Both foo and foo2 are erroneous. To be precise, the expected implicit conversion from scoped_array to bool is not allowed:
➜ /tmp clang++ --std=c++14 testconversion.cpp -o testconversion.o
testconversion.cpp:4:12: error: no viable conversion from returned value of type 'const boost::scoped_array<int>' to function return type 'bool'
return bar;
^~~
testconversion.cpp:8:16: error: no viable conversion from 'const boost::scoped_array<int>' to 'const bool'
const bool r = bar;
This brings up two questions:
when initializing a new object of type T2, including return statement in a function returning T2;
Look inside the documentation of boost::scoped_array:
operator unspecified-bool-type () const; // never throwsReturns an unspecified value that, when used in boolean contexts, is equivalent to
get() != 0.
You have to use static_cast to convert your boost::scoped_array to bool:
bool foo(const boost::scoped_array<int>& bar) {
return static_cast<bool>(bar);
}
bool foo2(const boost::scoped_array<int>& bar) {
const bool r = static_cast<bool>(bar);
return r;
}
Maybe just a typo but in your example you passing boost::scoped_array by value. It has no copy constructor, so passing it by value will also cause errors.
It works with Boost 1.48.0 because the operator_bool.hpp was different in that version. In Boost 1.64.0 the same header contains explicit operator bool () const; which prevenst you to copy-initialize a bool from a boost::scoped_array instance when you are compiling it with -std=c++14 (or -std=c++11). Your code will work with Boost 1.64.0 too if you are compiling it with -std=c++98.
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