resolved most todo and recompiled most examples and tests

test/specify/no_guard.cpp

@@ -0,0 +1,36 @@
+
+// Test missing contract guard gives run-time error.
+
+struct err {};
+#define BOOST_CONTRACT_ON_MISSING_GUARD { throw err(); }
+
+#include <boost/contract/function.hpp>
+#include <boost/contract/guard.hpp>
+#include <boost/detail/lightweight_test.hpp>
+
+int main() {
+    boost::contract::guard c = boost::contract::function() // Test this is OK.
+        .precondition([] {})
+        .old([] {})
+        .postcondition([] {})
+    ;
+
+    try {
+        boost::contract::function() // Test no `guard c = ...` errors.
+            .precondition([] {})
+            .old([] {})
+            .postcondition([] {})
+        ;
+        #if !defined(BOOST_CONTRACT_NO_PRECONDITIONS) || \
+                !defined(BOOST_CONTRACT_NO_POSTCONDITIONS) || \
+                !defined(BOOST_CONTRACT_NO_INVARIANTS)
+            BOOST_TEST(false); // Error, must throw.
+        #endif
+    } catch(err const&) {
+        // OK, threw as expected.
+    } catch(...) {
+        BOOST_TEST(false); // Error, unexpected throw.
+    }
+    return boost::report_errors();
+}
+