[BUG] `1 as std::string` errors

[JohelEGP]

Title: 1 as std::string errors.

Minimal reproducer (https://cpp2.godbolt.org/z/qdh9vWzod):

main: () = {
  _ = 1 as std::string;
}

Commands:

cppfront main.cpp2
clang++18 -std=c++23 -stdlib=libc++ -lc++abi -pedantic-errors -Wall -Wextra -Wconversion -Werror=unused-result -I . main.cpp

Expected result: Program returned: 0

Actual result and error:

Cpp2 lowered to Cpp1:

//=== Cpp2 type declarations ====================================================


#include "cpp2util.h"



//=== Cpp2 type definitions and function declarations ===========================

auto main() -> int;
  

//=== Cpp2 function definitions =================================================

auto main() -> int{
  static_cast<void>(cpp2::as_<std::string, 1>());
}

Output:

In file included from /app/build/main.cpp:6:
In file included from /app/cpp2util.h:1:
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1825:13: error: static assertion failed due to requirement 'program_violates_type_safety_guarantee<std::string, int>': No safe 'as' cast available - please check your cast
 1825 |             program_violates_type_safety_guarantee<C, CPP2_TYPEOF(x)>,
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
build/main.cpp:18:27: note: in instantiation of function template specialization 'cpp2::as_<std::string, 1>' requested here
   18 |   static_cast<void>(cpp2::as_<std::string, 1>());
      |                           ^
In file included from /app/build/main.cpp:6:
In file included from /app/cpp2util.h:1:
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1830:12: error: no matching function for call to 'as'
 1830 |     return as<C,x>();
      |            ^~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1104:23: note: candidate template ignored: constraints not satisfied [with C = std::string, x = 1]
 1104 | inline constexpr auto as() -> auto
      |                       ^
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1103:15: note: because 'std::is_arithmetic_v<std::string>' evaluated to false
 1103 |     requires (std::is_arithmetic_v<C> && std::is_arithmetic_v<CPP2_TYPEOF(x)>)
      |               ^
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1520:16: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1520 | constexpr auto as( X const& x ) -> decltype(auto)
      |                ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1474:16: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1474 | constexpr auto as( X const& x ) -> T
      |                ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1406:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1406 | auto as( std::variant<Ts...> const& x ) -> decltype(auto) {
      |      ^   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1381:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1381 | auto as( std::variant<Ts...> & x ) -> decltype(auto) {
      |      ^   ~~~~~~~~~~~~~~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1356:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1356 | auto as( std::variant<Ts...> && x ) -> decltype(auto) {
      |      ^   ~~~~~~~~~~~~~~~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1213:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1213 | auto as( X x ) -> C {
      |      ^   ~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1202:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1202 | auto as( X const& x ) -> C const& {
      |      ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1196:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1196 | auto as( X& x ) -> C& {
      |      ^   ~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1190:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1190 | auto as( X const& x ) -> C const& {
      |      ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1184:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1184 | auto as( X& x ) -> C& {
      |      ^   ~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1166:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1166 | auto as( X const& x ) -> auto
      |      ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1158:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1158 | auto as(X const& x) -> C
      |      ^  ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1152:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1152 | auto as( X& x ) -> decltype(auto) {
      |      ^   ~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1146:6: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1146 | auto as( X const& x ) -> decltype(auto) {
      |      ^   ~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1128:23: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1128 | inline constexpr auto as(auto const& x CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> auto
      |                       ^  ~~~~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1114:23: note: candidate function template not viable: requires single argument 'x', but no arguments were provided
 1114 | inline constexpr auto as(auto const& x) -> auto
      |                       ^  ~~~~~~~~~~~~~
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:1098:6: note: candidate function template not viable: requires 1 argument, but 0 were provided
 1098 | auto as(auto const&) -> auto {
      |      ^  ~~~~~~~~~~~
2 errors generated.

[leejy12]

What is the expected value of 1 as std::string?

[JohelEGP]

Like this: https://cpp2.godbolt.org/z/E7ebY9GYW.

main: () = {
  i :== 1;
  s := i as std::string;
  [[assert: s == "1"]]
}

Program returned: 0

[filipsajdak]

It was already fixed in #701

[JohelEGP]

Then you may add that to its opening comment so that this is automatically closed when that is merged.

[JohelEGP]

Now it works in the main branch.