Add is and as support for std::expected

Author: bluetarpmedia

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/test-results/msvc-2022-c++20/pure2-expected-is-as.cpp.output

@@ -0,0 +1,67 @@
+pure2-expected-is-as.cpp
+pure2-expected-is-as.cpp2(7): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(7): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(7): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(7): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(8): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(8): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(8): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(8): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(8): error C2660: 'unexpected': function does not take 1 arguments
+C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.41.34120\include\eh.h(33): note: see declaration of 'unexpected'
+pure2-expected-is-as.cpp2(8): note: while trying to match the argument list '(int)'
+pure2-expected-is-as.cpp2(8): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(9): error C2039: 'expected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(9): error C2275: 'std::string': expected an expression instead of a type
+pure2-expected-is-as.cpp2(9): error C2065: 'ex3': undeclared identifier
+pure2-expected-is-as.cpp2(9): error C2275: 'size_t': expected an expression instead of a type
+pure2-expected-is-as.cpp2(11): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(15): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(20): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(25): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(25): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(25): error C2059: syntax error: '>'
+pure2-expected-is-as.cpp2(25): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(30): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(34): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(39): error C2065: 'ex1': undeclared identifier
+pure2-expected-is-as.cpp2(39): error C2119: 'val1': the type for 'auto' cannot be deduced from an empty initializer
+pure2-expected-is-as.cpp2(42): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(47): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(52): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(57): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(57): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(57): error C2059: syntax error: '>'
+pure2-expected-is-as.cpp2(57): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(58): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(61): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(62): error C2065: 'ex2': undeclared identifier
+pure2-expected-is-as.cpp2(65): error C2039: 'unexpected': is not a member of 'std'
+predefined C++ types (compiler internal)(346): note: see declaration of 'std'
+pure2-expected-is-as.cpp2(65): error C2062: type 'int' unexpected
+pure2-expected-is-as.cpp2(65): error C2062: type 'unknown-type' unexpected
+pure2-expected-is-as.cpp2(65): error C2143: syntax error: missing ';' before '}'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ';' before '<<'
+pure2-expected-is-as.cpp2(66): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
+pure2-expected-is-as.cpp2(66): error C2371: 'std::cout': redefinition; different basic types
+C:\Program Files\Microsoft Visual Studio\2022\Professional\VC\Tools\MSVC\14.41.34120\include\iostream(39): note: see declaration of 'std::cout'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '<<'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ';' before '{'
+pure2-expected-is-as.cpp2(66): error C2447: '{': missing function header (old-style formal list?)
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '||'
+pure2-expected-is-as.cpp2(66): error C2065: 'Obj': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C2065: 'Params': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: '}'
+pure2-expected-is-as.cpp2(66): error C2143: syntax error: missing ')' before ';'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: 'requires'
+pure2-expected-is-as.cpp2(66): error C2059: syntax error: ')'
+pure2-expected-is-as.cpp2(66): error C2065: 'obj': undeclared identifier
+pure2-expected-is-as.cpp2(66): error C3553: decltype expects an expression not a type
+pure2-expected-is-as.cpp2(66): error C2065: 'params': undeclared identifier
+pure2-expected-is-as.cpp2(66): fatal error C1003: error count exceeds 100; stopping compilation

regression-tests/test-results/msvc-2022-c++latest/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

regression-tests/test-results/msvc-2022-c++latest/pure2-expected-is-as.cpp.output

@@ -0,0 +1 @@
+pure2-expected-is-as.cpp

regression-tests/test-results/pure2-expected-is-as.cpp

@@ -0,0 +1,117 @@
+
+#define CPP2_IMPORT_STD          Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-expected-is-as.cpp2"
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-expected-is-as.cpp2"
+// `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?).
+
+#line 5 "pure2-expected-is-as.cpp2"
+[[nodiscard]] auto main() -> int;
+
+#line 75 "pure2-expected-is-as.cpp2"
+auto test_inspect(auto const& x, auto const& msg) -> void;
+
+//=== Cpp2 function definitions =================================================
+
+#line 1 "pure2-expected-is-as.cpp2"
+
+#line 5 "pure2-expected-is-as.cpp2"
+[[nodiscard]] auto main() -> int{
+
+    std::expected<int,int> ex1 {123}; 
+    std::expected<int,int> ex2 {std::unexpected(-1)}; 
+    std::expected<std::string,size_t> ex3 {"Expect the unexpected"}; 
+
+    if (cpp2::impl::is<int>(ex1)) {
+        std::cout << "ex1 is int\n";
+    }
+
+    if (cpp2::impl::is<bool>(ex1)) {
+        std::cout << "BUG - ex1 is not a bool\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<void>(ex1)) {
+        std::cout << "BUG - ex1 is not 'empty'\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<std::unexpected<int>>(ex1)) {
+        std::cout << "BUG - ex1 is not unexpected\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is(ex1, 123)) {
+        std::cout << "ex1 is 123\n";
+    }
+
+    if (cpp2::impl::is(ex1, 100)) {
+        std::cout << "BUG - ex1's value is not 100\n";
+        return -1; 
+    }
+
+    auto val1 {cpp2::impl::as_<int>(ex1)}; 
+    std::cout << "ex1 as int = " << cpp2::move(val1) << "\n";
+
+    if (cpp2::impl::is<int>(ex2)) {
+        std::cout << "BUG - ex2 is not an int\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<bool>(ex2)) {
+        std::cout << "BUG - ex2 is not a bool\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is(ex2, 123)) {
+        std::cout << "BUG - ex2 does not have a value\n";
+        return -1; 
+    }
+
+    if (cpp2::impl::is<std::unexpected<int>>(ex2)) {
+        std::cout << "ex2 is unexpected<int> and error is: " << CPP2_UFCS(error)(ex2) << "\n";
+    }
+
+    if (cpp2::impl::is<void>(ex2)) {
+        std::cout << "ex2 is 'empty' aka unexpected<int> and error is: " << CPP2_UFCS(error)(ex2) << "\n";
+    }
+
+    auto ex2_err {cpp2::impl::as_<std::unexpected<int>>(ex2)}; 
+    std::cout << "ex2 as std::unexpected<int> and error = " << CPP2_UFCS(error)(cpp2::move(ex2_err)) << "\n";
+
+    test_inspect(cpp2::move(ex1), "expected<int, int> with value");
+    test_inspect(cpp2::move(ex2), "expected<int, int> with unexpected");
+    test_inspect(cpp2::move(ex3), "expected<string, size_t> with value");
+
+    return 0; 
+}
+
+#line 75 "pure2-expected-is-as.cpp2"
+auto test_inspect(auto const& x, auto const& msg) -> void{
+
+    auto unwrap {[](cpp2::impl::in<std::unexpected<int>> unexp) -> auto{
+        return CPP2_UFCS(error)(unexp); 
+    }}; 
+
+    std::cout 
+        << "\n" << msg << "\n    ..." 
+        << [&] () -> std::string { auto&& _expr = x;
+            if (cpp2::impl::is<int>(_expr)) { if constexpr( requires{"integer " + std::to_string(cpp2::impl::as<int>(x));} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("integer " + std::to_string(cpp2::impl::as<int>(x)))),std::string> ) return "integer " + std::to_string(cpp2::impl::as<int>(x)); else return std::string{}; else return std::string{}; }
+            else if (cpp2::impl::is<std::unexpected<int>>(_expr)) { if constexpr( requires{"unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x)));} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x))))),std::string> ) return "unexpected<int> " + std::to_string(cpp2::move(unwrap)(cpp2::impl::as<std::unexpected<int>>(x))); else return std::string{}; else return std::string{}; }
+            else if (cpp2::impl::is<std::string>(_expr)) { if constexpr( requires{"string " + cpp2::impl::as<std::string>(x);} ) if constexpr( std::is_convertible_v<CPP2_TYPEOF(("string " + cpp2::impl::as<std::string>(x))),std::string> ) return "string " + cpp2::impl::as<std::string>(x); else return std::string{}; else return std::string{}; }
+            else return " no match"; }
+        () 
+        << "\n";
+}
+

regression-tests/test-results/pure2-expected-is-as.cpp2.output

@@ -0,0 +1,2 @@
+pure2-expected-is-as.cpp2... ok (all Cpp2, passes safety checks)
+