scoped: add optional reset modifier

CMakeLists.txt

@@ -625,6 +625,7 @@ if (TESTS)
         rational
         region
         roots/bisection
+        scoped
         signal
         singleton
         stream

scoped.hpp

@@ -25,10 +25,15 @@ namespace cruft::scoped {
 
         ~restore ()
         {
-            m_target = m_value;
+            if (m_restore)
+                m_target = m_value;
         }
 
+        /// Disable restoration of the value.
+        void reset (void) { m_restore = false; }
+
     private:
+        bool m_restore = true;
         ValueT &m_target;
         ValueT const m_value;
     };

test/scoped.cpp

@@ -0,0 +1,35 @@
+#include "scoped.hpp"
+#include "tap.hpp"
+
+
+///////////////////////////////////////////////////////////////////////////////
+void test_restore (cruft::TAP::logger &tap)
+{
+    int value = 42;
+
+    {
+        cruft::scoped::restore raii (value);
+        tap.expect_eq (value, 42, "restorer constructor doesn't modifier value");
+        value = 7;
+    }
+
+    tap.expect_eq (value, 42, "restorer restores value at destruction");
+
+
+    {
+        cruft::scoped::restore raii (value);
+        value = 7;
+        raii.reset ();
+    }
+
+    tap.expect_eq (value, 7, "restorer reset doesn't modify value at destruction");
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+int main ()
+{
+    cruft::TAP::logger tap;
+    test_restore (tap);
+    return tap.status ();
+}