Add is and as support for std::expected (v2)

include/cpp2util.h

@@ -2078,6 +2078,93 @@ constexpr auto as( X&& x ) -> decltype(auto) {
 }
 
 
+
+//-------------------------------------------------------------------------------------------------------------
+//  std::expected is and as
+//
+#ifdef __cpp_lib_expected
+
+//  is Type
+//
+template<typename T, typename X>
+    requires std::is_same_v<X, std::expected<T, typename X::error_type>>
+constexpr auto is(X const& x) -> bool
+{
+    return x.has_value();
+}
+
+template<typename T, typename U, typename V>
+    requires std::is_same_v<T, empty>
+constexpr auto is(std::expected<U, V> const& x) -> bool
+{
+    return !x.has_value();
+}
+
+//  is std::unexpected<T> Type
+//
+template<typename T, typename X>
+    requires (
+        std::is_same_v<T, std::unexpected<typename X::error_type>>
+        && std::is_same_v<X, std::expected<typename X::value_type, typename X::error_type>>
+    )
+constexpr auto is(X const& x) -> bool
+{
+    return !x.has_value();
+}
+
+
+//  is Value
+//
+template<typename T, typename U>
+constexpr auto is(std::expected<T, U> const& x, auto&& value) -> bool
+{
+    //  Predicate case
+    if constexpr (requires{ bool{ value(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 }; }) {
+        return x.has_value() && x.value() == value;
+    }
+    else {
+        return false;
+    }
+}
+
+
+//  as
+//
+template<typename T, typename X>
+    requires std::is_same_v<X, std::expected<T, typename X::error_type>>
+constexpr auto as(X const& x) -> decltype(auto)
+{
+    return x.value();
+}
+
+//  as std::unexpected<T>
+//
+template<typename T, typename X>
+    requires (
+        std::is_same_v<T, std::unexpected<typename X::error_type>>
+        && std::is_same_v<X, std::expected<typename X::value_type, typename X::error_type>>
+    )
+constexpr auto as(X const& x) -> decltype(auto)
+{
+    // It's UB to call `error` if `has_value` is true.
+    if (x.has_value()) {
+        Throw(
+            std::runtime_error("Cannot cast 'expected' to 'unexpected' because it has a value"),
+            "Cannot cast 'expected' to 'unexpected' because it has a value");
+    }
+
+    return std::unexpected<typename X::error_type>(x.error());
+}
+#endif
+
 } // impl
 
 

regression-tests/pure2-expected-is-as.cpp2

@@ -0,0 +1,90 @@
+// `std::expected` requires C++23 so a dedicated test file is needed
+// since only MSVC supports it at time of writing, and there's no #ifdef
+// or `static if` support in Cpp2 (yet?).
+
+main: () -> int = {
+
+    ex1: std::expected<int, int> = (123);
+    ex2: std::expected<int, int> = std::unexpected(-1);
+    ex3: std::expected<std::string, size_t> = ("Expect the unexpected");
+
+    if ex1 is int {
+        std::cout << "ex1 is int\n";
+    }
+
+    if ex1 is bool {
+        std::cout << "BUG - ex1 is not a bool\n";
+        return -1;
+    }
+
+    if ex1 is void {
+        std::cout << "BUG - ex1 is not 'empty'\n";
+        return -1;
+    }
+
+    if ex1 is std::unexpected<int> {
+        std::cout << "BUG - ex1 is not unexpected\n";
+        return -1;
+    }
+
+    if ex1 is 123 {
+        std::cout << "ex1 is 123\n";
+    }
+
+    if ex1 is 100 {
+        std::cout << "BUG - ex1's value is not 100\n";
+        return -1;
+    }
+
+    val1:= ex1 as int;
+    std::cout << "ex1 as int = " << val1 << "\n";
+
+    if ex2 is int {
+        std::cout << "BUG - ex2 is not an int\n";
+        return -1;
+    }
+
+    if ex2 is bool {
+        std::cout << "BUG - ex2 is not a bool\n";
+        return -1;
+    }
+
+    if ex2 is 123 {
+        std::cout << "BUG - ex2 does not have a value\n";
+        return -1;
+    }
+
+    if ex2 is std::unexpected<int> {
+        std::cout << "ex2 is unexpected<int> and error is: " << ex2.error() << "\n";
+    }
+
+    if ex2 is void {
+        std::cout << "ex2 is 'empty' aka unexpected<int> and error is: " << ex2.error() << "\n";
+    }
+
+    ex2_err:= ex2 as std::unexpected<int>;
+    std::cout << "ex2 as std::unexpected<int> and error = " << ex2_err.error() << "\n";
+
+    test_inspect(ex1, "expected<int, int> with value");
+    test_inspect(ex2, "expected<int, int> with unexpected");
+    test_inspect(ex3, "expected<string, size_t> with value");
+
+    return 0;
+}
+
+test_inspect: ( x: _, msg: _ ) = {
+
+    unwrap:= :(unexp: std::unexpected<int>) -> _ = {
+        return unexp.error();
+    };
+
+    std::cout
+        << "\n" << msg << "\n    ..."
+        << inspect x -> std::string {
+            is int = "integer " + std::to_string(x as int);
+            is std::unexpected<int> = "unexpected<int> " + std::to_string(unwrap(x as std::unexpected<int>));
+            is std::string = "string " + x as std::string;
+            is _   = " no match";
+        }
+        << "\n";
+}

regression-tests/run-tests.sh

@@ -135,28 +135,11 @@ if [ -z "$label" ]; then
     usage
 fi
 
-tests=$(ls | grep ".cpp2$")
-if [[ -n "$chosen_tests" ]]; then
-    for test in $chosen_tests; do
-        if ! [[ -f "$test" ]]; then
-            echo "Requested test ($test) not found"
-            exit 1
-        fi
-    done
-    echo "Performing tests:"
-    for test in $chosen_tests; do
-        echo "    $test"
-    done
-    echo
-    tests="$chosen_tests"
-else
-    printf "Performing all regression tests\n\n"
-fi
-
-expected_results_dir="test-results"
-
 ################
 # Get the directory with the exec outputs and compilation command
+# We also allow each compiler configuration to specify any test files(s) to exclude from running.
+expected_results_dir="test-results"
+exclude_test_filter=""
 if [[ "$cxx_compiler" == *"cl.exe"* ]]; then
     compiler_cmd="cl.exe -nologo -std:${cxx_std} -MD -EHsc -I ..\..\..\include -Fe:"
     exec_out_dir="$expected_results_dir/msvc-2022-${cxx_std}"
@@ -174,6 +157,12 @@ else
     if [[ "$compiler_version" == *"Apple clang version 14.0"* ||
           "$compiler_version" == *"Homebrew clang version 15.0"* ]]; then
         exec_out_dir="$expected_results_dir/apple-clang-14"
+        # We share the expected results dir for these two compilers, but there is one
+        # test which (as expected) fails to compile on both compilers, but has a slightly
+        # different error diagnostic because the clang path differs. So we exclude it from
+        # running. The alternative would be to duplicate the expected results files, which
+        # seems wasteful for just one test (that doesn't even compile).
+        exclude_test_filter="pure2-expected-is-as.cpp2"
     elif [[ "$compiler_version" == *"Apple clang version 15.0"* ]]; then
         exec_out_dir="$expected_results_dir/apple-clang-15"
     elif [[ "$compiler_version" == *"clang version 12.0"* ]]; then 
@@ -236,6 +225,30 @@ else
     exit 2
 fi
 
+################
+# Get the list of .cpp2 test files
+if [[ -n "$exclude_test_filter" ]]; then
+    tests=$(ls | grep ".cpp2$" | grep -v $exclude_test_filter)
+else
+    tests=$(ls | grep ".cpp2$")
+fi
+if [[ -n "$chosen_tests" ]]; then
+    for test in $chosen_tests; do
+        if ! [[ -f "$test" ]]; then
+            echo "Requested test ($test) not found"
+            exit 1
+        fi
+    done
+    echo "Performing tests:"
+    for test in $chosen_tests; do
+        echo "    $test"
+    done
+    echo
+    tests="$chosen_tests"
+else
+    printf "Performing all regression tests\n\n"
+fi
+
 ################
 cppfront_cmd="cppfront.exe"
 echo "Building cppfront"

regression-tests/test-results/apple-clang-14-c++2b/pure2-expected-is-as.cpp.output

@@ -0,0 +1,63 @@
+pure2-expected-is-as.cpp2:7:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex1 {123}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:7:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex1 {123}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:8:10: error: no member named 'expected' in namespace 'std'
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:8:22: error: expected '(' for function-style cast or type construction
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+                  ~~~^
+pure2-expected-is-as.cpp2:9:10: error: no member named 'expected' in namespace 'std'
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+    ~~~~~^
+pure2-expected-is-as.cpp2:9:30: error: expected '(' for function-style cast or type construction
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+                  ~~~~~~~~~~~^
+pure2-expected-is-as.cpp2:11:29: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<int>(ex1)) {
+                            ^
+pure2-expected-is-as.cpp2:15:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<bool>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:20:30: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is<void>(ex1)) {
+                             ^
+pure2-expected-is-as.cpp2:25:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                       ~~~~~^
+pure2-expected-is-as.cpp2:25:43: error: expected '(' for function-style cast or type construction
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                       ~~~^
+pure2-expected-is-as.cpp2:25:46: error: use of undeclared identifier 'ex1'; did you mean 'exp'?
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+                                             ^~~
+                                             exp
+/Applications/Xcode_14.3.1.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/math.h:895:1: note: 'exp' declared here
+exp(_A1 __lcpp_x) _NOEXCEPT {return ::exp((double)__lcpp_x);}
+^
+pure2-expected-is-as.cpp2:30:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:34:24: error: use of undeclared identifier 'ex1'
+    if (cpp2::impl::is(ex1, 100)) {
+                       ^
+pure2-expected-is-as.cpp2:39:37: error: use of undeclared identifier 'ex1'
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+                                    ^
+pure2-expected-is-as.cpp2:42:29: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<int>(ex2)) {
+                            ^
+pure2-expected-is-as.cpp2:47:30: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is<bool>(ex2)) {
+                             ^
+pure2-expected-is-as.cpp2:52:24: error: use of undeclared identifier 'ex2'
+    if (cpp2::impl::is(ex2, 123)) {
+                       ^
+pure2-expected-is-as.cpp2:57:29: error: no member named 'unexpected' in namespace 'std'
+    if (cpp2::impl::is<std::unexpected<int>>(ex2)) {
+                       ~~~~~^
+fatal error: too many errors emitted, stopping now [-ferror-limit=]
+20 errors generated.

regression-tests/test-results/apple-clang-15-c++2b/pure2-expected-is-as.cpp.execution

@@ -0,0 +1,15 @@
+ex1 is int
+ex1 is 123
+ex1 as int = 123
+ex2 is unexpected<int> and error is: -1
+ex2 is 'empty' aka unexpected<int> and error is: -1
+ex2 as std::unexpected<int> and error = -1
+
+expected<int, int> with value
+    ...integer 123
+
+expected<int, int> with unexpected
+    ...unexpected<int> -1
+
+expected<string, size_t> with value
+    ...string Expect the unexpected