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Move use of declval into decltype. #3

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merged 2 commits into from
Feb 23, 2024
Merged

Move use of declval into decltype. #3

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2db590a
Attempt 1: move declval into decltype only, take args in result_type_…
nickpdemarco Feb 23, 2024
dd7a22c
:art: Committing clang-format changes
Feb 23, 2024
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41 changes: 19 additions & 22 deletions test/initial_draft.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,8 @@
#include <stlab/concurrency/await.hpp>
#include <stlab/concurrency/future.hpp>

#define STLAB_FWD(x) std::forward<decltype(x)>(x)

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function-like macro 'STLAB_FWD' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage,-warnings-as-errors]

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function-like macro 'STLAB_FWD' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage,-warnings-as-errors]

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function-like macro 'STLAB_FWD' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage,-warnings-as-errors]

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function-like macro 'STLAB_FWD' used; consider a 'constexpr' template function [cppcoreguidelines-macro-usage,-warnings-as-errors]

/*

If exception inside of a segment _apply_ function throws an exception then the exception must be
Expand All @@ -30,7 +32,7 @@
*/

template <class Applicator, class... Fs>
class segment {

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class 'segment' defines a copy constructor, a copy assignment operator, a move constructor and a move assignment operator but does not define a destructor [cppcoreguidelines-special-member-functions,hicpp-special-member-functions,-warnings-as-errors]

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class 'segment' defines a copy constructor, a copy assignment operator, a move constructor and a move assignment operator but does not define a destructor [cppcoreguidelines-special-member-functions,hicpp-special-member-functions,-warnings-as-errors]

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class 'segment' defines a copy constructor, a copy assignment operator, a move constructor and a move assignment operator but does not define a destructor [cppcoreguidelines-special-member-functions,hicpp-special-member-functions,-warnings-as-errors]

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class 'segment' defines a copy constructor, a copy assignment operator, a move constructor and a move assignment operator but does not define a destructor [cppcoreguidelines-special-member-functions,hicpp-special-member-functions,-warnings-as-errors]
std::tuple<Fs...> _functions;
Applicator _apply;

Expand All @@ -49,13 +51,13 @@
The basic operations should follow those from C++ lambdas, for now default everything.
and see if the compiler gets it correct.
*/
explicit segment(const segment&) = default;

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copy constructor should not be declared explicit [hicpp-explicit-conversions,-warnings-as-errors]

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copy constructor should not be declared explicit [hicpp-explicit-conversions,-warnings-as-errors]

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copy constructor should not be declared explicit [hicpp-explicit-conversions,-warnings-as-errors]

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copy constructor should not be declared explicit [hicpp-explicit-conversions,-warnings-as-errors]
segment(segment&&) noexcept = default;
segment& operator=(const segment&) = default;
segment& operator=(segment&&) noexcept = default;

template <class F>
auto append(F&& f) && {

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parameter name 'f' is too short, expected at least 3 characters [readability-identifier-length,-warnings-as-errors]

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parameter name 'f' is too short, expected at least 3 characters [readability-identifier-length,-warnings-as-errors]

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parameter name 'f' is too short, expected at least 3 characters [readability-identifier-length,-warnings-as-errors]

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parameter name 'f' is too short, expected at least 3 characters [readability-identifier-length,-warnings-as-errors]
return chains::segment{std::move(_apply), std::tuple_cat(std::move(_functions),
std::tuple{std::forward<F>(f)})};
}
Expand All @@ -80,7 +82,7 @@

std::move(_apply)(
[_f = tuple_compose(std::move(_functions)),
_receiver = receiver](auto&&... args) mutable noexcept {

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declaration of ‘auto:60&& ... args’ shadows a parameter [-Wshadow]

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declaration of ‘auto:60&& ... args’ shadows a parameter [-Wshadow]

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declaration of ‘auto:60&& ... args’ shadows a parameter [-Wshadow]
if (_receiver.canceled()) return;
try {
std::move(_f)(std::forward<decltype(args)>(args)...);
Expand All @@ -92,6 +94,16 @@
}
};

namespace detail {

/// Apply a recursive lambda to each element in the tuple-like Segments.
template <class Fold, class Segments>
constexpr auto fold_over(Fold fold, Segments&& segments) {
return std::apply([fold](auto&&... links) { return fold(fold, STLAB_FWD(links)...); }, STLAB_FWD(segments));
}

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} // namespace detail

template <class Segment, class... Args>
using segment_result_type =
decltype(std::declval<Segment>().result_type_helper(std::declval<Args>()...));
Expand All @@ -100,32 +112,16 @@
simplify this code by handing the multi-argument case earlier (somehow).
*/

#define STLAB_FWD(x) std::forward<decltype(x)>(x)

template <class Tail, class Applicator, class... Fs>
class chain {
Tail _tail;
segment<Applicator, Fs...> _head;

/// Apply a recursive lambda to each element in _tail, followed by _head.
template <class F>
auto fold_over(F fold) && {
return std::apply([fold](auto&&... links) { return fold(fold, STLAB_FWD(links)...); },
std::tuple_cat(std::move(_tail), std::tuple(std::move(_head))));
}

template <class F>
static consteval auto static_fold_over(F fold) {
return std::apply([fold](auto&&... links) { return fold(fold, STLAB_FWD(links)...); },
std::tuple_cat(std::declval<Tail>(),
std::tuple(std::declval<segment<Applicator, Fs...>>())));
}

/// Return a lambda with the signature of
/// head( tail<n>( tail<1>( tail<0>( auto&& args... ) ) ) )
/// for computing the result type of this chain.
static consteval auto result_type_helper() {
return static_fold_over([](auto fold, auto&& first, auto&&... rest) {
static consteval auto result_type_helper(Tail&& tail, segment<Applicator, Fs...>&& head) {
return detail::fold_over([](auto fold, auto&& first, auto&&... rest) {
if constexpr (sizeof...(rest) == 0) {
return [_segment = STLAB_FWD(first)](auto&&... args) mutable {
return std::move(_segment).result_type_helper(STLAB_FWD(args)...);
Expand All @@ -136,12 +132,12 @@
return std::move(_segment).result_type_helper(STLAB_FWD(args)...);
};
}
});
}, std::tuple_cat(std::move(tail), std::tuple{std::move(head)}));
}

template <class R>
auto expand(const R& receiver) && {
return std::move(*this).fold_over([receiver](auto fold, auto&& first, auto&&... rest) {
return detail::fold_over([receiver](auto fold, auto&& first, auto&&... rest) {
if constexpr (sizeof...(rest) == 0) {
return [receiver,
_segment = STLAB_FWD(first).append(receiver)](auto&&... args) mutable {
Expand All @@ -153,12 +149,13 @@
return std::move(_segment).invoke(receiver, STLAB_FWD(args)...);
};
}
});
}, std::tuple_cat(std::move(_tail), std::tuple{std::move(_head)}));
}

public:
template <class... Args>
using result_type = decltype(result_type_helper()(std::declval<Args>()...));
using result_type =
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@sean-parent this is my best attempt at getting result_type to work, so far. If I try to use result_type_helper like this:

    template <class... Args>
    using result_type = 
      decltype(std::declval<chain>().result_type_helper()(std::declval<Args>()...));

We fail by attempting to access a member of an incomplete type. Not sure if there's a cleaner way around this.

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I'm liking it! What more would you like to do on this before I push.

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If you're happy, I'm happy. Feel free to merge.

decltype(result_type_helper(std::declval<Tail>(), std::declval<segment<Applicator, Fs...>>())(std::declval<Args>()...));

explicit chain(Tail&& tail, segment<Applicator, Fs...>&& head)
: _tail{std::move(tail)}, _head{std::move(head)} {}
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