mirror of
https://github.com/PurpleI2P/Boost-for-Android-Prebuilt
synced 2025-01-08 22:08:01 +00:00
386 lines
12 KiB
C++
386 lines
12 KiB
C++
/*=============================================================================
|
|
Copyright (c) 2014 Paul Fultz II
|
|
reveal.h
|
|
Distributed under the Boost Software License, Version 1.0. (See accompanying
|
|
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
|
|
==============================================================================*/
|
|
|
|
#ifndef BOOST_HOF_GUARD_FUNCTION_REVEAL_H
|
|
#define BOOST_HOF_GUARD_FUNCTION_REVEAL_H
|
|
|
|
/// reveal
|
|
/// ======
|
|
///
|
|
/// Description
|
|
/// -----------
|
|
///
|
|
/// The `reveal` function adaptor helps shows the error messages that get
|
|
/// masked on some compilers. Sometimes an error in a function that causes a
|
|
/// substitution failure, will remove the function from valid overloads. On
|
|
/// compilers without a backtrace for substitution failure, this will mask the
|
|
/// error inside the function. The `reveal` adaptor will expose these error
|
|
/// messages while still keeping the function SFINAE-friendly.
|
|
///
|
|
/// Sample
|
|
/// ------
|
|
///
|
|
/// If we take the `print` example from the quick start guide like this:
|
|
///
|
|
/// namespace adl {
|
|
///
|
|
/// using std::begin;
|
|
///
|
|
/// template<class R>
|
|
/// auto adl_begin(R&& r) BOOST_HOF_RETURNS(begin(r));
|
|
/// }
|
|
///
|
|
/// BOOST_HOF_STATIC_LAMBDA_FUNCTION(for_each_tuple) = [](const auto& sequence, auto f) BOOST_HOF_RETURNS
|
|
/// (
|
|
/// boost::hof::unpack(boost::hof::proj(f))(sequence)
|
|
/// );
|
|
///
|
|
/// auto print = boost::hof::fix(boost::hof::first_of(
|
|
/// [](auto, const auto& x) -> decltype(std::cout << x, void())
|
|
/// {
|
|
/// std::cout << x << std::endl;
|
|
/// },
|
|
/// [](auto self, const auto& range) -> decltype(self(*adl::adl_begin(range)), void())
|
|
/// {
|
|
/// for(const auto& x:range) self(x);
|
|
/// },
|
|
/// [](auto self, const auto& tuple) -> decltype(for_each_tuple(tuple, self), void())
|
|
/// {
|
|
/// return for_each_tuple(tuple, self);
|
|
/// }
|
|
/// ));
|
|
///
|
|
/// Which prints numbers and vectors:
|
|
///
|
|
/// print(5);
|
|
///
|
|
/// std::vector<int> v = { 1, 2, 3, 4 };
|
|
/// print(v);
|
|
///
|
|
/// However, if we pass a type that can't be printed, we get an error like
|
|
/// this:
|
|
///
|
|
/// print.cpp:49:5: error: no matching function for call to object of type 'boost::hof::fix_adaptor<boost::hof::first_of_adaptor<(lambda at print.cpp:29:9), (lambda at print.cpp:33:9), (lambda at print.cpp:37:9)> >'
|
|
/// print(foo{});
|
|
/// ^~~~~
|
|
/// fix.hpp:158:5: note: candidate template ignored: substitution failure [with Ts = <foo>]: no matching function for call to object of type 'const boost::hof::first_of_adaptor<(lambda at
|
|
/// print.cpp:29:9), (lambda at print.cpp:33:9), (lambda at print.cpp:37:9)>'
|
|
/// operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
|
|
///
|
|
/// Which is short and gives very little information why it can't be called.
|
|
/// It doesn't even show the overloads that were try. However, using the
|
|
/// `reveal` adaptor we can get more info about the error like this:
|
|
///
|
|
/// print.cpp:49:5: error: no matching function for call to object of type 'boost::hof::reveal_adaptor<boost::hof::fix_adaptor<boost::hof::first_of_adaptor<(lambda at print.cpp:29:9), (lambda at print.cpp:33:9),
|
|
/// (lambda at print.cpp:37:9)> >, boost::hof::fix_adaptor<boost::hof::first_of_adaptor<(lambda at print.cpp:29:9), (lambda at print.cpp:33:9), (lambda at print.cpp:37:9)> > >'
|
|
/// boost::hof::reveal(print)(foo{});
|
|
/// ^~~~~~~~~~~~~~~~~~
|
|
/// reveal.hpp:149:20: note: candidate template ignored: substitution failure [with Ts = <foo>, $1 = void]: no matching function for call to object of type '(lambda at print.cpp:29:9)'
|
|
/// constexpr auto operator()(Ts&&... xs) const
|
|
/// ^
|
|
/// reveal.hpp:149:20: note: candidate template ignored: substitution failure [with Ts = <foo>, $1 = void]: no matching function for call to object of type '(lambda at print.cpp:33:9)'
|
|
/// constexpr auto operator()(Ts&&... xs) const
|
|
/// ^
|
|
/// reveal.hpp:149:20: note: candidate template ignored: substitution failure [with Ts = <foo>, $1 = void]: no matching function for call to object of type '(lambda at print.cpp:37:9)'
|
|
/// constexpr auto operator()(Ts&&... xs) const
|
|
/// ^
|
|
/// fix.hpp:158:5: note: candidate template ignored: substitution failure [with Ts = <foo>]: no matching function for call to object of type 'const boost::hof::first_of_adaptor<(lambda at
|
|
/// print.cpp:29:9), (lambda at print.cpp:33:9), (lambda at print.cpp:37:9)>'
|
|
/// operator()(Ts&&... xs) const BOOST_HOF_SFINAE_RETURNS
|
|
///
|
|
/// So now the error has a note for each of the lambda overloads it tried. Of
|
|
/// course this can be improved even further by providing custom reporting of
|
|
/// failures.
|
|
///
|
|
/// Synopsis
|
|
/// --------
|
|
///
|
|
/// template<class F>
|
|
/// reveal_adaptor<F> reveal(F f);
|
|
///
|
|
/// Requirements
|
|
/// ------------
|
|
///
|
|
/// F must be:
|
|
///
|
|
/// * [ConstInvocable](ConstInvocable)
|
|
/// * MoveConstructible
|
|
///
|
|
/// Reporting Failures
|
|
/// ------------------
|
|
///
|
|
/// By default, `reveal` reports the substitution failure by trying to call
|
|
/// the function. However, more detail expressions can be be reported from a
|
|
/// template alias by using `as_failure`. This is done by defining a nested
|
|
/// `failure` struct in the function object and then inheriting from
|
|
/// `as_failure`. Also multiple failures can be reported by using
|
|
/// `with_failures`.
|
|
///
|
|
/// Synopsis
|
|
/// --------
|
|
///
|
|
/// // Report failure by instantiating the Template
|
|
/// template<template<class...> class Template>
|
|
/// struct as_failure;
|
|
///
|
|
/// // Report multiple falures
|
|
/// template<class... Failures>
|
|
/// struct with_failures;
|
|
///
|
|
/// // Report the failure for each function
|
|
/// template<class... Fs>
|
|
/// struct failure_for;
|
|
///
|
|
/// // Get the failure of a function
|
|
/// template<class F>
|
|
/// struct get_failure;
|
|
///
|
|
/// Example
|
|
/// -------
|
|
///
|
|
/// #include <boost/hof.hpp>
|
|
/// #include <cassert>
|
|
///
|
|
/// struct sum_f
|
|
/// {
|
|
/// template<class T, class U>
|
|
/// using sum_failure = decltype(std::declval<T>()+std::declval<U>());
|
|
///
|
|
/// struct failure
|
|
/// : boost::hof::as_failure<sum_failure>
|
|
/// {};
|
|
///
|
|
/// template<class T, class U>
|
|
/// auto operator()(T x, U y) const BOOST_HOF_RETURNS(x+y);
|
|
/// };
|
|
///
|
|
/// int main() {
|
|
/// assert(sum_f()(1, 2) == 3);
|
|
/// }
|
|
///
|
|
|
|
#include <boost/hof/always.hpp>
|
|
#include <boost/hof/returns.hpp>
|
|
#include <boost/hof/is_invocable.hpp>
|
|
#include <boost/hof/identity.hpp>
|
|
#include <boost/hof/detail/move.hpp>
|
|
#include <boost/hof/detail/callable_base.hpp>
|
|
#include <boost/hof/detail/delegate.hpp>
|
|
#include <boost/hof/detail/holder.hpp>
|
|
#include <boost/hof/detail/join.hpp>
|
|
#include <boost/hof/detail/make.hpp>
|
|
#include <boost/hof/detail/static_const_var.hpp>
|
|
#include <boost/hof/detail/using.hpp>
|
|
|
|
#ifndef BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS
|
|
#ifdef __clang__
|
|
#define BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS 1
|
|
#else
|
|
#define BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS 0
|
|
#endif
|
|
#endif
|
|
|
|
namespace boost { namespace hof {
|
|
|
|
namespace detail {
|
|
|
|
|
|
template<class T, class=void>
|
|
struct has_failure
|
|
: std::false_type
|
|
{};
|
|
|
|
template<class T>
|
|
struct has_failure<T, typename holder<
|
|
typename T::failure
|
|
>::type>
|
|
: std::true_type
|
|
{};
|
|
|
|
struct identity_failure
|
|
{
|
|
template<class T>
|
|
T operator()(T&& x);
|
|
|
|
template<class T>
|
|
static T&& val();
|
|
#if BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS
|
|
template<template<class...> class Template, class... Ts>
|
|
BOOST_HOF_USING(defer, Template<Ts...>);
|
|
#else
|
|
template<template<class...> class Template, class... Ts>
|
|
static auto defer(Ts&&...) -> Template<Ts...>;
|
|
#endif
|
|
|
|
};
|
|
|
|
}
|
|
|
|
template<class F, class=void>
|
|
struct get_failure
|
|
{
|
|
template<class... Ts>
|
|
struct of
|
|
{
|
|
#if BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS
|
|
template<class Id>
|
|
using apply = decltype(Id()(std::declval<F>())(std::declval<Ts>()...));
|
|
#else
|
|
template<class Id>
|
|
static auto apply(Id id) -> decltype(id(std::declval<F>())(std::declval<Ts>()...));
|
|
#endif
|
|
};
|
|
};
|
|
|
|
template<class F>
|
|
struct get_failure<F, typename std::enable_if<detail::has_failure<F>::value>::type>
|
|
: F::failure
|
|
{};
|
|
|
|
template<template<class...> class Template>
|
|
struct as_failure
|
|
{
|
|
template<class... Ts>
|
|
struct of
|
|
{
|
|
#if BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS
|
|
template<class Id>
|
|
using apply = typename Id::template defer<Template, Ts...>;
|
|
#else
|
|
template<class Id>
|
|
static auto apply(Id) -> decltype(Id::template defer<Template, Ts...>());
|
|
#endif
|
|
};
|
|
};
|
|
|
|
namespace detail {
|
|
template<class Failure, class... Ts>
|
|
BOOST_HOF_USING_TYPENAME(apply_failure, Failure::template of<Ts...>);
|
|
|
|
template<class F, class Failure>
|
|
struct reveal_failure
|
|
{
|
|
// Add default constructor to make clang 3.4 happy
|
|
constexpr reveal_failure()
|
|
{}
|
|
// This is just a placeholder to produce a note in the compiler, it is
|
|
// never called
|
|
template<
|
|
class... Ts,
|
|
class=typename std::enable_if<(!is_invocable<F, Ts...>::value)>::type
|
|
>
|
|
constexpr auto operator()(Ts&&... xs) const
|
|
#if BOOST_HOF_REVEAL_USE_TEMPLATE_ALIAS
|
|
-> typename apply_failure<Failure, Ts...>::template apply<boost::hof::detail::identity_failure>;
|
|
#else
|
|
-> decltype(apply_failure<Failure, Ts...>::apply(boost::hof::detail::identity_failure()));
|
|
#endif
|
|
};
|
|
|
|
template<class F, class Failure=get_failure<F>, class=void>
|
|
struct traverse_failure
|
|
: reveal_failure<F, Failure>
|
|
{
|
|
constexpr traverse_failure()
|
|
{}
|
|
};
|
|
|
|
template<class F, class Failure>
|
|
struct traverse_failure<F, Failure, typename holder<
|
|
typename Failure::children
|
|
>::type>
|
|
: Failure::children::template overloads<F>
|
|
{
|
|
constexpr traverse_failure()
|
|
{}
|
|
};
|
|
|
|
template<class Failure, class Transform, class=void>
|
|
struct transform_failures
|
|
: Transform::template apply<Failure>
|
|
{};
|
|
|
|
template<class Failure, class Transform>
|
|
struct transform_failures<Failure, Transform, typename holder<
|
|
typename Failure::children
|
|
>::type>
|
|
: Failure::children::template transform<Transform>
|
|
{};
|
|
|
|
}
|
|
|
|
template<class Failure, class... Failures>
|
|
struct failures;
|
|
|
|
template<class... Fs>
|
|
struct with_failures
|
|
{
|
|
typedef BOOST_HOF_JOIN(failures, Fs...) children;
|
|
};
|
|
|
|
template<class Failure, class... Failures>
|
|
struct failures
|
|
{
|
|
template<class Transform>
|
|
BOOST_HOF_USING(transform, with_failures<detail::transform_failures<Failure, Transform>, detail::transform_failures<Failures, Transform>...>);
|
|
|
|
template<class F, class FailureBase=BOOST_HOF_JOIN(failures, Failures...)>
|
|
struct overloads
|
|
: detail::traverse_failure<F, Failure>, FailureBase::template overloads<F>
|
|
{
|
|
constexpr overloads()
|
|
{}
|
|
using detail::traverse_failure<F, Failure>::operator();
|
|
using FailureBase::template overloads<F>::operator();
|
|
};
|
|
};
|
|
|
|
template<class Failure>
|
|
struct failures<Failure>
|
|
{
|
|
template<class Transform>
|
|
BOOST_HOF_USING(transform, with_failures<detail::transform_failures<Failure, Transform>>);
|
|
|
|
template<class F>
|
|
BOOST_HOF_USING(overloads, detail::traverse_failure<F, Failure>);
|
|
};
|
|
|
|
template<class Transform, class... Fs>
|
|
struct failure_map
|
|
: with_failures<detail::transform_failures<get_failure<Fs>, Transform>...>
|
|
{};
|
|
|
|
template<class... Fs>
|
|
struct failure_for
|
|
: with_failures<get_failure<Fs>...>
|
|
{};
|
|
|
|
template<class F, class Base=detail::callable_base<F>>
|
|
struct reveal_adaptor
|
|
: detail::traverse_failure<Base>, Base
|
|
{
|
|
typedef reveal_adaptor fit_rewritable1_tag;
|
|
using detail::traverse_failure<Base>::operator();
|
|
using Base::operator();
|
|
|
|
BOOST_HOF_INHERIT_CONSTRUCTOR(reveal_adaptor, Base);
|
|
};
|
|
// Avoid double reveals, it causes problem on gcc 4.6
|
|
template<class F>
|
|
struct reveal_adaptor<reveal_adaptor<F>>
|
|
: reveal_adaptor<F>
|
|
{
|
|
typedef reveal_adaptor fit_rewritable1_tag;
|
|
BOOST_HOF_INHERIT_CONSTRUCTOR(reveal_adaptor, reveal_adaptor<F>);
|
|
};
|
|
|
|
BOOST_HOF_DECLARE_STATIC_VAR(reveal, detail::make<reveal_adaptor>);
|
|
|
|
}} // namespace boost::hof
|
|
|
|
#endif
|