From 61534ca3adda0e214d6fb7dd9bc4173edb6e02d1 Mon Sep 17 00:00:00 2001
From: Nicholas Londey <nicholas@londey.com>
Date: Wed, 22 Apr 2020 10:09:13 +1000
Subject: [PATCH] Changed implementation of gsl::narrow to throw
 gsl::narrowing_error Implementation now behaves as described in the C++ Core
 Guidlines

---
 include/gsl/gsl_util  |  8 ++++++--
 tests/utils_tests.cpp | 12 +++---------
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index d1f7f33..bc65923 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -96,6 +96,10 @@ constexpr T narrow_cast(U&& u) noexcept
     return static_cast<T>(std::forward<U>(u));
 }
 
+struct narrowing_error : public std::exception
+{
+};
+
 namespace details
 {
     template <class T, class U>
@@ -115,9 +119,9 @@ constexpr
 T narrow(U u) noexcept(false)
 {
     T t = narrow_cast<T>(u);
-    if (static_cast<U>(t) != u) gsl::details::terminate();
+    if (static_cast<U>(t) != u) throw narrowing_error{};
     if (!details::is_same_signedness<T, U>::value && ((t < T{}) != (u < U{})))
-        gsl::details::terminate();
+        throw narrowing_error{};
     return t;
 }
 
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index f7f7ce3..98faf58 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -104,11 +104,6 @@ TEST(utils_tests, narrow_cast)
 
 TEST(utils_tests, narrow)
 {
-    std::set_terminate([] {
-        std::cerr << "Expected Death. narrow";
-        std::abort();
-    });
-
     int n = 120;
     const char c = narrow<char>(n);
     EXPECT_TRUE(c == 120);
@@ -123,14 +118,13 @@ TEST(utils_tests, narrow)
     EXPECT_TRUE(narrow<uint32_t>(int32_t(1)) == 1);
     EXPECT_TRUE(narrow<uint32_t>(int32_max) == static_cast<uint32_t>(int32_max));
 
-    EXPECT_DEATH(narrow<uint32_t>(int32_t(-1)), deathstring);
-    EXPECT_DEATH(narrow<uint32_t>(int32_min), deathstring);
+    EXPECT_THROW(narrow<uint32_t>(int32_t(-1)), narrowing_error);
+    EXPECT_THROW(narrow<uint32_t>(int32_min), narrowing_error);
 
     n = -42;
-    EXPECT_DEATH(narrow<unsigned>(n), deathstring);
+    EXPECT_THROW(narrow<unsigned>(n), narrowing_error);
 
 #if GSL_CONSTEXPR_NARROW
     static_assert(narrow<char>(120) == 120, "Fix GSL_CONSTEXPR_NARROW");
 #endif
-
 }