[lmi-commits] [lmi] master dd32674: Show values and types when bourn_cast cannot preserve value

[Greg Chicares]

branch: master
commit dd3267482cdfab4e09689fb61d26c335f0f163ca
Author: Gregory W. Chicares <address@hidden>
Commit: Gregory W. Chicares <address@hidden>

    Show values and types when bourn_cast cannot preserve value
---
 bourn_cast.hpp      | 16 +++++++++++++++-
 bourn_cast_test.cpp |  2 +-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/bourn_cast.hpp b/bourn_cast.hpp
index 358952f..c0021c7 100644
--- a/bourn_cast.hpp
+++ b/bourn_cast.hpp
@@ -24,8 +24,11 @@
 
 #include "config.hpp"
 
+#include "rtti_lmi.hpp"                 // lmi::TypeInfo [demangling]
+
 #include <cmath>                        // isinf(), isnan(), signbit()
 #include <limits>
+#include <sstream>
 #include <stdexcept>
 
 /// Numeric stinted cast, across whose bourn no value is returned.
@@ -135,7 +138,18 @@ inline To bourn_cast(From from)
             throw std::runtime_error("Cast would transgress upper limit.");
         To const r = static_cast<To>(from);
         if(r != from)
-            throw std::runtime_error("Cast would not preserve value.");
+            {
+            lmi::TypeInfo from_type(typeid(From));
+            lmi::TypeInfo   to_type(typeid(To  ));
+            std::ostringstream oss;
+            oss.setf(std::ios_base::fixed, std::ios_base::floatfield);
+            oss
+                << "Cast from " << from << " [" << from_type << "]"
+                << " to "       << r    << " [" << to_type   << "]"
+                << " would not preserve value."
+                ;
+            throw std::runtime_error(oss.str());
+            }
         return r;
         }
 
diff --git a/bourn_cast_test.cpp b/bourn_cast_test.cpp
index 31a413b..a2bb52c 100644
--- a/bourn_cast_test.cpp
+++ b/bourn_cast_test.cpp
@@ -394,7 +394,7 @@ void test_conv_fpint(char const* file, int line)
     BOOST_TEST_THROW
         (bourn_cast<I>(F(3.14))
         ,std::runtime_error
-        ,"Cast would not preserve value."
+        ,lmi_test::what_regex("^Cast.*would not preserve value\\.$")
         );
 #else  // defined TEST_BOOST_CAST_INSTEAD
     // boost::numeric cast truncates whereas bourn_cast throws; both