Fix consteval not working as member func sometimes

Author: prevter

include/slic.hpp

@@ -353,7 +353,7 @@ namespace slic {
             #define ANSI_BOLDLINE ANSI_BOLD ANSI_UNDERLINE
 
             if constexpr (requires { T::Description; }) {
-                std::cout << T::Description << '\n';
+                std::cout << T::Description << "\n\n";
             }
 
             std::cout << ANSI_BOLDLINE "Usage:" ANSI_RESET " " << m_programName;
@@ -362,8 +362,8 @@ namespace slic {
                 std::cout << " [OPTIONS]";
             }
 
-            forEachArg([](auto const& arg) {
-                if constexpr (arg.isOptional()) {
+            forEachArg([]<typename A>(A const& arg) {
+                if constexpr (A::isOptional()) {
                     std::cout << " [" << arg.name() << ']';
                 } else {
                     std::cout << " <" << arg.name() << '>';
@@ -391,14 +391,14 @@ namespace slic {
             if constexpr (optionCount() > 0) {
                 std::cout << "\n" ANSI_BOLDLINE "Options:" ANSI_RESET "\n";
 
-                forEachOption([](auto const& opt) {
+                forEachOption([]<typename O>(O const& opt) {
                     if (opt.altName().empty()) {
                         std::cout << "  " ANSI_BOLD << opt.name() << ANSI_RESET;
                     } else {
                         std::cout << "  " ANSI_BOLD << opt.altName() << ", " << opt.name() << ANSI_RESET;
                     }
 
-                    if constexpr (opt.needsValue()) {
+                    if constexpr (O::needsValue()) {
                         std::cout << " <value>";
                     }
 
@@ -589,4 +589,4 @@ namespace slic {
     };
 } // namespace slic
 
-#endif // SLIC_ARG_PARSER_HPP
+#endif // SLIC_ARG_PARSER_HPP