an example/test uses a dangling reference

Start with libs/local_function/test/return_assign.cpp and run the existing test to compare the temporary and local-variable cases. Trace how the returned boost::function retains the bound reference, then determine the intended safe test behavior; done means the example no longer relies on a dangling reference and the relevant lifetime case is correctly covered.

libs/local_function/test/return_assign.cpp uses a dangling reference:

#include <boost/local_function.hpp>
#include <boost/function.hpp>
#include <boost/detail/lightweight_test.hpp>
#include <iostream>

//[return_assign
void call1(boost::function<int (int) > f) { BOOST_TEST(f(1) == 5); }
void call0(boost::function<int (void)> f) { BOOST_TEST(f() == 5); }

boost::function<int (int, int)> linear(const int& slope) {
    int BOOST_LOCAL_FUNCTION(const bind& slope,
            int x, default 1, int y, default 2) {
        return x + slope * y;
    } BOOST_LOCAL_FUNCTION_NAME(lin)

    boost::function<int (int, int)> f = lin; // Assign to local variable.
    BOOST_TEST(f(1, 2) == 5);

    call1(lin); // Pass to other functions.
    call0(lin);

    return lin; // Return.
}

void call(void) {
    boost::function<int (int, int)> f = linear(2); // create temporary, bind reference to temporary
    BOOST_TEST(f(1, 2) == 5); // !!!!!!!!!!!!!!!!!!!!!!!! use the reference
}
//]

int main(void) {
    call();
    return boost::report_errors();
}

changing the target from temporary to local variable can let the test fail:

#include <boost/local_function.hpp>
#include <boost/function.hpp>
#include <boost/detail/lightweight_test.hpp>
#include <iostream>

//[return_assign
void call1(boost::function<int(int) > f) { BOOST_TEST(f(1) == 5); }
void call0(boost::function<int(void)> f) { BOOST_TEST(f() == 5); }

boost::function<int(int, int)> linear(const int& slope) {
    int BOOST_LOCAL_FUNCTION(const bind & slope,
        int x, default 1, int y, default 2) {
        return x + slope * y;
    } BOOST_LOCAL_FUNCTION_NAME(lin)

        boost::function<int(int, int)> f = lin; // Assign to local variable.
    BOOST_TEST(f(1, 2) == 5);

    call1(lin); // Pass to other functions.
    call0(lin);

    return lin; // Return.
}

void call1(void) {
    boost::function<int(int, int)> f = linear(2);
    BOOST_TEST(f(1, 2) == 5); // !!!!!!!!!!!!!!!!!!!!!!!! test passed, although dangling reference
}
void call2(void) {
    int a = 2;
    boost::function<int(int, int)> f = linear(a);
    a = 3;
    BOOST_TEST(f(1, 2) == 5); // !!!!!!!!!!!!!!!!!!!!!!!! test failed
}
//]

int main(void) {
    call1();
    call2();
    return boost::report_errors();
}