1 files changed, 41 insertions, 0 deletions
diff --git a/src/boost/libs/contract/example/features/old.cpp b/src/boost/libs/contract/example/features/old.cpp
new file mode 100644
index 000000000..bdf8b8c6e
--- /dev/null
+++ b/src/boost/libs/contract/example/features/old.cpp
@@ -0,0 +1,41 @@
+
+// Copyright (C) 2008-2018 Lorenzo Caminiti
+// Distributed under the Boost Software License, Version 1.0 (see accompanying
+// file LICENSE_1_0.txt or a copy at http://www.boost.org/LICENSE_1_0.txt).
+// See: http://www.boost.org/doc/libs/release/libs/contract/doc/html/index.html
+
+#include <boost/contract.hpp>
+#include <string>
+#include <cassert>
+
+//[old
+char replace(std::string& s, unsigned index, char x) {
+    char result;
+    boost::contract::old_ptr<char> old_char; // Null, old value copied later...
+    boost::contract::check c = boost::contract::function()
+        .precondition([&] {
+            BOOST_CONTRACT_ASSERT(index < s.size());
+        })
+        .old([&] { // ...after preconditions (and invariants) checked.
+            old_char = BOOST_CONTRACT_OLDOF(s[index]);
+        })
+        .postcondition([&] {
+            BOOST_CONTRACT_ASSERT(s[index] == x);
+            BOOST_CONTRACT_ASSERT(result == *old_char);
+        })
+    ;
+
+    result = s[index];
+    s[index] = x;
+    return result;
+}
+//]
+
+int main() {
+    std::string s = "abc";
+    char r = replace(s, 1, '_');
+    assert(s == "a_c");
+    assert(r == 'b');
+    return 0;
+}
+