Provide support for explicit operator bool (foonathan#79)

flexorx · May 26, 2018 · 367f2dc · 367f2dc
1 parent 9ed89d6
commit 367f2dc
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diff --git a/include/type_safe/strong_typedef.hpp b/include/type_safe/strong_typedef.hpp
@@ -464,6 +464,18 @@ namespace type_safe
         TYPE_SAFE_DETAIL_MAKE_STRONG_TYPEDEF_OP(division, /)
         TYPE_SAFE_DETAIL_MAKE_STRONG_TYPEDEF_OP(modulo, %)
 
+        template <class StrongTypedef>
+        struct explicit_bool
+        {
+            /// \exclude
+            explicit constexpr operator bool() const
+            {
+                return static_cast<bool>(
+                    detail::get_underlying<StrongTypedef>(
+                        static_cast<const StrongTypedef&>(*this)));
+            }
+        };
+
         template <class StrongTypedef>
         struct increment
         {

diff --git a/test/strong_typedef.cpp b/test/strong_typedef.cpp
@@ -573,4 +573,40 @@ TEST_CASE("strong_typedef")
         in >> a;
         REQUIRE(static_cast<int>(a) == 1);
     }
+    SECTION("explicit bool")
+    {
+        struct type : strong_typedef<type, int>,
+                      strong_typedef_op::explicit_bool<type>
+        {
+            using strong_typedef::strong_typedef;
+        };
+
+        type a(0);
+        REQUIRE(!a);
+        type b(1);
+        REQUIRE(b);
+    }
+    SECTION("explicit bool nonconstexpr")
+    {
+        struct foo
+        {
+            bool flag;
+
+            explicit operator bool() const
+            {
+                return flag;
+            }
+        };
+
+        struct type : strong_typedef<type, foo>,
+                      strong_typedef_op::explicit_bool<type>
+        {
+            using strong_typedef::strong_typedef;
+        };
+
+        type a(foo{false});
+        REQUIRE(!a);
+        type b(foo{true});
+        REQUIRE(b);
+    }
 }