is()/as(): refactor is() and as() for std::optional

Author: filipsajdak

include/cpp2util.h

@@ -2103,29 +2103,26 @@ constexpr auto as( X && x ) -> decltype(auto) {
 
 //  is Type
 //
-template<typename T, typename X>
-    requires std::is_same_v<X,std::optional<T>>
-constexpr auto is( X const& x ) -> bool
-    { return x.has_value(); }
-
-template<typename T, typename U>
-    requires std::is_same_v<T,empty>
-constexpr auto is( std::optional<U> const& x ) -> bool
-    { return !x.has_value(); }
-
+template<typename T, specialization_of_template<std::optional> X>
+constexpr auto is( X const& x ) -> bool { 
+    if (!x.has_value()) {
+        return std::same_as<T, empty>;
+    }
+    if constexpr (requires { static_cast<const T&>(*x);}) {
+        return true;
+    }
+    return false;
+}
 
 //  is Value
 //
 template<typename T>
 constexpr auto is( std::optional<T> const& x, auto&& value ) -> bool
 {
     //  Predicate case
-    if constexpr (requires{ bool{ value(x) }; }) {
+    if constexpr (valid_predicate<decltype(value), decltype(x)>) {
         return value(x);
     }
-    else if constexpr (std::is_function_v<decltype(value)> || requires{ &value.operator(); }) {
-        return false;
-    }
 
     //  Value case
     else if constexpr (requires{ bool{ x.value() == value }; }) {
@@ -2137,10 +2134,15 @@ constexpr auto is( std::optional<T> const& x, auto&& value ) -> bool
 
 //  as
 //
-template<typename T, typename X>
-    requires std::is_same_v<X,std::optional<T>>
-constexpr auto as( X const& x ) -> decltype(auto)
-    { return x.value(); }
+template<typename T, specialization_of_template<std::optional> X>
+constexpr auto as( X&& x ) -> decltype(auto) { 
+    constness_like_t<T, X>* ptr = nullptr;
+    if constexpr (requires { static_cast<const T&>(*x); }) {
+        ptr = &static_cast<const T&>(*x);
+    }
+    if (!ptr) { Throw( std::bad_optional_access(), "'as' cast failed for 'std::optional'"); }
+    return cpp2::forward_like<X>(*ptr);
+}
 
 
 } // impl