Revert "externals: Update boost to 1.72 and add Boost Context"

boost/safe_numerics/checked_result.hpp

@@ -0,0 +1,146 @@
+#ifndef BOOST_NUMERIC_CHECKED_RESULT
+#define BOOST_NUMERIC_CHECKED_RESULT
+
+//  Copyright (c) 2012 Robert Ramey
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+// contains operations for doing checked aritmetic on NATIVE
+// C++ types.
+#include <cassert>
+#include <type_traits> // is_convertible
+#include "exception.hpp"
+
+namespace boost {
+namespace safe_numerics {
+
+template<typename R>
+struct checked_result {
+    const safe_numerics_error m_e;
+    const union {
+        R m_r;
+        char const * m_msg;
+    };
+    
+    // don't permit construction without initial value;
+    checked_result() = delete;
+
+    // note: I implemented the following non-default copy and move
+    // constructors because I thought I needed to do this in order
+    // to make them constexpr.  Turns out though that doing this creates
+    // a syntax error because the assignment results in error due
+    // to assignment "outside of object lifetime".  I think this could
+    // be addressed by replacing the anonymous union above with a
+    // named union.  This would create some syntax changes which would
+    // ripple through some parts of th program.  So for now, we'll just
+    // rely on the default copy and move constructors.
+    #if 0
+    // copy constructor
+    constexpr /*explicit*/ checked_result(const checked_result & r) noexpect :
+        m_e(r.m_e)
+    {
+        if(safe_numerics_error::success == r.m_e)
+            m_r = r.m_r;
+        else
+            m_msg = r.m_msg;
+    }
+
+    // move constructor
+    constexpr /*explicit*/ checked_result(checked_result && r) noexcept :
+        m_e(r.m_e)
+    {
+        if(safe_numerics_error::success == r.m_e)
+            m_r = r.m_r;
+        else
+            m_msg = r.m_msg;
+    }
+    #endif
+    checked_result(const checked_result & r) = default;
+    checked_result(checked_result && r) = default;
+    
+    constexpr /*explicit*/ checked_result(const R & r) :
+        m_e(safe_numerics_error::success),
+        m_r(r)
+    {}
+    #if 0
+    template<typename T>
+    constexpr /*explicit*/ checked_result(const T & t) noexcept :
+        m_e(safe_numerics_error::success),
+        m_r(t)
+    {}
+    #endif
+    constexpr /*explicit*/ checked_result(
+        const safe_numerics_error & e,
+        const char * msg = ""
+    )  noexcept :
+        m_e(e),
+        m_msg(msg)
+    {
+        assert(m_e != safe_numerics_error::success);
+    }
+    // permit construct from another checked result type
+    template<typename T>
+    constexpr /*explicit*/ checked_result(const checked_result<T> & t) noexcept :
+        m_e(t.m_e)
+    {
+        static_assert(
+            std::is_convertible<T, R>::value,
+            "T must be convertible to R"
+        );
+        if(safe_numerics_error::success == t.m_e)
+            m_r = t.m_r;
+        else
+            m_msg = t.m_msg;
+    }
+    constexpr bool exception() const {
+        return m_e != safe_numerics_error::success;
+    }
+
+    // accesors
+    constexpr operator R() const  noexcept{
+        // don't assert here.  Let the library catch these errors
+        assert(! exception());
+        return m_r;
+    }
+    
+    constexpr operator safe_numerics_error () const  noexcept{
+        // note that this is a legitimate operation even when
+        // the operation was successful - it will return success
+        return m_e;
+    }
+    constexpr operator const char *() const  noexcept{
+        assert(exception());
+        return m_msg;
+    }
+
+    // disallow assignment
+    checked_result & operator=(const checked_result &) = delete;
+};
+
+#if 0
+template<typename R>
+constexpr checked_result<R> make_checked_result(
+    const safe_numerics_error & e,
+    char const * const & m
+)  noexcept {
+    return checked_result<R>(e, m);
+}
+#endif
+
+template <class R>
+class make_checked_result {
+public:
+    template<safe_numerics_error E>
+    constexpr static checked_result<R> invoke(
+        char const * const & m
+    ) noexcept {
+        return checked_result<R>(E, m);
+    }
+};
+
+} // safe_numerics
+} // boost
+
+#endif  // BOOST_NUMERIC_CHECKED_RESULT