Better compiler error messages when assigning incompatible `Tasks`
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CodingCanuck commented
This compiles just fine:
#include <memory>
#include <string>
#include "eventuals/grpc/client.h"
#include "eventuals/grpc/completion-pool.h"
#include "eventuals/task.h"
#include "eventuals/then.h"
#include "grpcpp/security/credentials.h"
#include "stout/borrowed_ptr.h"
::eventuals::Task::Of<void>::With<::eventuals::grpc::Client> my_method(
const std::string& target,
const std::shared_ptr<::grpc::ChannelCredentials>& credentials,
stout::borrowed_ptr<::eventuals::grpc::CompletionPool> pool) {
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
::eventuals::grpc::Client(target, credentials, std::move(pool)),
[](::eventuals::grpc::Client& client) {
return ::eventuals::Then([]() {});
});
}But if you drop the ::With<> bit from the return type:
#include <memory>
#include <string>
#include "eventuals/grpc/client.h"
#include "eventuals/grpc/completion-pool.h"
#include "eventuals/task.h"
#include "eventuals/then.h"
#include "grpcpp/security/credentials.h"
#include "stout/borrowed_ptr.h"
::eventuals::Task::Of<void> my_method( // Different return type!
const std::string& target,
const std::shared_ptr<::grpc::ChannelCredentials>& credentials,
stout::borrowed_ptr<::eventuals::grpc::CompletionPool> pool) {
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
::eventuals::grpc::Client(target, credentials, std::move(pool)),
[](::eventuals::grpc::Client& client) {
return ::eventuals::Then([]() {});
});
}It fails to compile with an error that's very difficult to understand, complaining about bad callables and lambdas being too large for a callback:
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:329:7: error: static_assert failed due to requirement 'std::is_invocable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>::value' "'Task' expects a callable (e.g., a lambda) that takes no arguments"
static_assert(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:350:7: error: static_assert failed due to requirement 'sizeof (f) <= SIZEOF_CALLBACK' "'Task' expects a callable (e.g., a lambda) that can be captured in a 'Callback'"
static_assert(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:1:
In file included from /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/memory:76:
In file included from /usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/unique_ptr.h:37:
/usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/tuple:1858:14: error: no matching function for call to '__invoke'
return std::__invoke(std::forward<_Fn>(__f),
^~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/tuple:1869:19: note: in instantiation of function template specialization 'std::__apply_impl<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client> &, std::tuple<> &>' requested here
return std::__apply_impl(std::forward<_Fn>(__f),
^
external/com_github_3rdparty_eventuals/eventuals/task.h:355:31: note: in instantiation of function template specialization 'std::apply<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client> &, std::tuple<> &>' requested here
using E = decltype(std::apply(f, args_));
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
/usr/lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/invoke.h:90:5: note: candidate template ignored: substitution failure [with _Callable = eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client> &, _Args = <>]: no type named 'type' in 'std::__invoke_result<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client> &>'
__invoke(_Callable&& __fn, _Args&&... __args)
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:357:7: error: static_assert failed due to requirement 'std::is_void_v<int> || HasValueFrom<int, void>::value' "'Task' expects a callable (e.g., a lambda) that returns an eventual but you're returning a value"
static_assert(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:371:7: error: static_assert failed due to requirement 'tuple_types_subset_subtype_v<int, std::tuple<>>' "Specified errors can't be raised within 'Task'"
static_assert(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:375:7: error: static_assert failed due to requirement 'std::disjunction_v<std::is_same<int, eventuals::_TaskFailure>, std::is_convertible<int, void>>' "eventual result type can not be converted into type of 'Task'"
static_assert(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:393:43: error: type 'typename std::remove_reference<_Task<void, void, tuple<>, Client> &>::type' (aka 'eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>') does not provide a call operator
new HeapTask<E, From_, To_>(f(args...)),
^
external/com_github_3rdparty_eventuals/eventuals/task.h:127:47: error: member reference base type 'int' is not a structure or union
using Adapted_ = decltype(std::declval<E_>().template k<From_>(
~~~~~~~~~~~~~~~~~~^ ~
external/com_github_3rdparty_eventuals/eventuals/task.h:403:14: note: in instantiation of template class 'eventuals::HeapTask<int, void, void>' requested here
e->Start(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:102:13: error: member reference base type 'eventuals::HeapTask<int, void, void>::Adapted_' (aka 'int') is not a structure or union
adapted_.Register(interrupt);
~~~~~~~~^~~~~~~~~
external/com_github_3rdparty_eventuals/eventuals/task.h:411:16: note: in instantiation of member function 'eventuals::HeapTask<int, void, void>::Fail' requested here
e->Fail(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:104:13: error: member reference base type 'eventuals::HeapTask<int, void, void>::Adapted_' (aka 'int') is not a structure or union
adapted_.Fail(std::move(exception));
~~~~~~~~^~~~~
external/com_github_3rdparty_eventuals/eventuals/task.h:118:13: error: member reference base type 'eventuals::HeapTask<int, void, void>::Adapted_' (aka 'int') is not a structure or union
adapted_.Register(interrupt);
~~~~~~~~^~~~~~~~~
external/com_github_3rdparty_eventuals/eventuals/task.h:419:16: note: in instantiation of member function 'eventuals::HeapTask<int, void, void>::Stop' requested here
e->Stop(
^
external/com_github_3rdparty_eventuals/eventuals/task.h:511:7: note: in instantiation of function template specialization 'eventuals::_TaskFromToWith::Composable<void, void, std::tuple<>>::Composable<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
: e_(std::move(args)..., std::move(f)) {}
^
respect/keep_alive/keep_alive_rpc_handler.cc:15:10: note: in instantiation of function template specialization 'eventuals::_Task<void, void, std::tuple<>>::_Task<eventuals::_Task<void, void, std::tuple<>, eventuals::grpc::Client>>' requested here
return ::eventuals::Task::Of<void>::With<::eventuals::grpc::Client>(
^
In file included from respect/keep_alive/keep_alive_rpc_handler.cc:6:
external/com_github_3rdparty_eventuals/eventuals/task.h:120:13: error: member reference base type 'eventuals::HeapTask<int, void, void>::Adapted_' (aka 'int') is not a structure or union
adapted_.Stop();
~~~~~~~~^~~~~
It would be much better to instead return an error like "Can't assign A to B", or "No overload of operator=() found".