NamedType: validate in ++ and --

the mess here is to make sure that the new value is valid without
changing the old value, to make sure that the value stays valid even when
an exception is thrown

fixes #192

include/adm/detail/named_type.hpp

@@ -112,7 +112,10 @@ namespace adm {
       }
 
       NamedType<T, Tag, Validator>& operator++() {
-        ++value_;
+        T tmp = value_;
+        tmp++;
+        Validator::validate(tmp);
+        value_ = std::move(tmp);
         return *this;
       }
 
@@ -123,7 +126,10 @@ namespace adm {
       }
 
       NamedType<T, Tag, Validator>& operator--() {
-        --value_;
+        T tmp = value_;
+        tmp--;
+        Validator::validate(tmp);
+        value_ = std::move(tmp);
         return *this;
       }
 

tests/named_type_tests.cpp

@@ -52,6 +52,16 @@ TEST_CASE("NamedType_range_check") {
   NamedIntegerRange goodValue(5);
   REQUIRE_THROWS_AS(NamedIntegerRange(12), OutOfRangeError);
   REQUIRE_THROWS_AS(NamedIntegerRange(-1), OutOfRangeError);
+
+  NamedIntegerRange lower_limit(0);
+  REQUIRE_THROWS_AS(lower_limit--, OutOfRangeError);
+  REQUIRE_THROWS_AS(--lower_limit, OutOfRangeError);
+  REQUIRE(lower_limit == 0);
+
+  NamedIntegerRange upper_limit(10);
+  REQUIRE_THROWS_AS(upper_limit++, OutOfRangeError);
+  REQUIRE_THROWS_AS(++upper_limit, OutOfRangeError);
+  REQUIRE(upper_limit == 10);
 }
 
 TEST_CASE("screen_edge_validator") {