Explicit value_type for ConfigOptionProxy (#1251)

src/util/ConfigManager/ConfigOptionProxy.h

@@ -34,8 +34,6 @@ class ConfigOptionProxyImplementation {
   ConfigOptionType* option_;
 
  public:
-  using Type = T;
-
   // Custom constructor.
   explicit ConfigOptionProxyImplementation(ConfigOptionType& opt)
       : option_(&opt) {
@@ -81,6 +79,9 @@ class ConstConfigOptionProxy
       ConfigManagerImpl::ConfigOptionProxyImplementation<T, const ConfigOption>;
 
  public:
+  using value_type = T;
+
+  // Construct proxy for the given option.
   explicit ConstConfigOptionProxy(const ConfigOption& opt) : Base(opt) {}
 };
 
@@ -94,6 +95,9 @@ class ConfigOptionProxy
       ConfigManagerImpl::ConfigOptionProxyImplementation<T, ConfigOption>;
 
  public:
+  using value_type = T;
+
+  // Construct proxy for the given option.
   explicit ConfigOptionProxy(ConfigOption& opt) : Base(opt) {}
 
   // Implicit conversion from not const to const is allowed.

test/ConfigOptionProxyTest.cpp

@@ -11,6 +11,7 @@
 #include "../test/util/GTestHelpers.h"
 #include "util/ConfigManager/ConfigOption.h"
 #include "util/ConfigManager/ConfigOptionProxy.h"
+#include "util/TypeTraits.h"
 
 namespace ad_utility {
 
@@ -21,16 +22,16 @@ namespace ad_utility {
 @tparam OptionType Exists to define, if the test should be done with
 `ConfigOption`, or `const ConfigOption`.
 */
-template <template <typename> typename ProxyType, typename OptionType>
-requires std::same_as<OptionType, ConfigOption> ||
-         std::same_as<OptionType, const ConfigOption>
+template <template <typename> typename ProxyType,
+          SameAsAny<ConfigOption, const ConfigOption> OptionType>
 void basicConstructorTest() {
   // Test construction for a given type.
   auto doTest = []<typename T>() {
     // Does the normal constructor work?
     T varForConfigOption;
     OptionType opt("testOption", "", &varForConfigOption);
     ASSERT_EQ(&opt, &ProxyType<T>(opt).getConfigOption());
+    static_assert(std::same_as<T, typename ProxyType<T>::value_type>);
 
     // Is there an exception, if we give a config option of the wrong type?
     doForTypeInConfigOptionValueType([&opt]<typename WrongT>() {