finished very first draft of reference docs

test/function/check_if.cpp

@@ -0,0 +1,59 @@
+
+// Test assertions skipped when operations to check them missing (e.g., `==`).
+
+#include <boost/contract/function.hpp>
+#include <boost/contract/guard.hpp>
+#include <boost/contract/assert.hpp>
+#include <boost/contract/call_if.hpp>
+#include <boost/bind.hpp>
+#include <boost/type_traits/has_equal_to.hpp>
+#include <boost/detail/lightweight_test.hpp>
+#include <functional>
+#include <vector>
+
+unsigned equal_skips;
+
+template<typename T>
+void push_back(std::vector<T>& vect, T const& val) {
+    boost::contract::guard c = boost::contract::function()
+        .postcondition([&] {
+            BOOST_CONTRACT_ASSERT(
+                boost::contract::call_if<boost::has_equal_to<T> >(
+                    boost::bind(std::equal_to<T>(), boost::cref(vect.back()),
+                            boost::cref(val))
+                ).else_([] { ++equal_skips; return true; })
+            );
+        })
+    ;
+    vect.push_back(val);
+}
+
+struct j { // Type without operator==.
+    explicit j(int i) : j_(i) {}
+private:
+    int j_;
+};
+
+int main() {
+    std::vector<int> vi;
+    equal_skips = 0;
+    push_back(vi, 123);
+    BOOST_TEST_EQ(equal_skips, 0);
+        
+    unsigned const cnt =
+        #ifndef BOOST_CONTRACT_NO_POSTCONDITIONS
+            1
+        #else
+            0
+        #endif
+    ;
+
+    j jj(456);
+    std::vector<j> vj;
+    equal_skips = 0;
+    push_back(vj, jj);
+    BOOST_TEST_EQ(equal_skips, cnt);
+
+    return boost::report_errors();
+}
+