Avoid use of C++17 constexpr

src/string-container.h

@@ -12,15 +12,20 @@ Required because List does not support subscript operator, GDExtension PackedStr
 #include "defs.h"
 
 namespace {
-    template <typename, typename = void> struct has_subscript_operator: std::false_type {};
-    template <typename T> struct has_subscript_operator<T, std::void_t<decltype(std::declval<T&>()[std::declval<size_t>()])>>: std::true_type {};
+  template <typename, typename = void> struct has_subscript_operator: std::false_type {};
+  template <typename T> struct has_subscript_operator<T, std::void_t<decltype(std::declval<T&>()[std::declval<size_t>()])>>: std::true_type {};
+  template <typename, typename = void> struct has_get_method: std::false_type {};
+  template <typename T> struct has_get_method<T, std::void_t<decltype(std::declval<T&>().get(std::declval<size_t>()))>>: std::true_type {};
 }
 
-namespace godot{
-    template <typename T> String string_container_get(T container, const int i) {
-        if constexpr (has_subscript_operator<T>::value) return container[i];
-        else return container.get(i);
-    }
+namespace godot {
+  template <typename T> typename std::enable_if<has_subscript_operator<T>::value, String>::type string_container_get(T container, const uint32_t i) {
+    return container[i];
+  }
+
+  template <typename T> typename std::enable_if<has_get_method<T>::value && !has_subscript_operator<T>::value, String>::type string_container_get(T container, const uint32_t i) {
+    return container.get(i);
+  }
 }
 
 #endif