From fbfdacb45f7961efe1e2bbbcebbf081f77c6c9a3 Mon Sep 17 00:00:00 2001
From: Damian Jarek <damian.jarek93@gmail.com>
Date: Tue, 28 Mar 2017 23:53:49 +0200
Subject: [PATCH] Enable usage of gsl::narrow with exceptions disabled

This solution uses the approach of boost::asio to enabling usage of the
library in environments where exception usage is either prohibited
or not feasible (due to code size constraints). A function template
gsl::throw_exception has been added, which in a normal environment just
throws the exception. However, when GSL_TERMINATE_ON_CONTRACT_VIOLATION
is defined the function is only declared by gsl and the definition of
this function template must be supplied by the library's user.

Closes: #468

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>
---
 include/gsl/gsl_assert | 42 +++++++++++++++++++++++++++++++++++++++---
 include/gsl/gsl_util   |  4 ++--
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/include/gsl/gsl_assert b/include/gsl/gsl_assert
index 43da231..2c9cb8d 100644
--- a/include/gsl/gsl_assert
+++ b/include/gsl/gsl_assert
@@ -72,19 +72,55 @@ struct fail_fast : public std::logic_error
 {
     explicit fail_fast(char const* const message) : std::logic_error(message) {}
 };
-}
+namespace details
+{
+template <typename Exception>
+[[noreturn]] void throw_exception(Exception&& exception);
+
+} //namespace details
+} //namespace gsl
 
 #if defined(GSL_THROW_ON_CONTRACT_VIOLATION)
 
+namespace gsl
+{
+namespace details
+{
+template <typename Exception>
+[[noreturn]] void throw_exception(Exception&& exception)
+{
+    throw exception;
+}
+
+} //namespace details
+} //namespace gsl
+
 #define GSL_CONTRACT_CHECK(type, cond)                                                             \
     (GSL_LIKELY(cond) ? static_cast<void>(0)                                                       \
-                      : throw gsl::fail_fast("GSL: " type " failure at " __FILE__                  \
-                                             ": " GSL_STRINGIFY(__LINE__)))
+                      : gsl::throw_exception(gsl::fail_fast("GSL: " type " failure at " __FILE__   \
+                                             ": " GSL_STRINGIFY(__LINE__))))
 
 #elif defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION)
 
 #define GSL_CONTRACT_CHECK(type, cond) (GSL_LIKELY(cond) ? static_cast<void>(0) : std::terminate())
 
+namespace gsl
+{
+namespace details
+{
+template <typename Exception>
+[[noreturn]] void throw_exception(Exception&& exception)
+{
+    static_cast<void>(exception);
+    std::terminate();
+}
+
+} //namespace details
+} //namespace gsl
+
+ #define GSL_CONTRACT_CHECK(type, cond)                                                            \
+    (GSL_LIKELY(cond) ? static_cast<void>(0) : std::terminate())
+
 #elif defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION)
 
 #define GSL_CONTRACT_CHECK(type, cond) GSL_ASSUME(cond)
diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index 7f3218d..0d7a09c 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -121,9 +121,9 @@ template <class T, class U>
 inline T narrow(U u)
 {
     T t = narrow_cast<T>(u);
-    if (static_cast<U>(t) != u) throw narrowing_error();
+    if (static_cast<U>(t) != u) gsl::details::throw_exception(narrowing_error());
     if (!details::is_same_signedness<T, U>::value && ((t < T{}) != (u < U{})))
-        throw narrowing_error();
+        gsl::details::throw_exception(narrowing_error());
     return t;
 }