libcruft-util/introspection.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2015-2017 Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include "std.hpp"
#include "algo/search.hpp"

#include <cruft/util/preprocessor.hpp>

#include <algorithm>
#include <array>
#include <cstddef>
#include <cstdint>
#include <ostream>
#include <string>
#include <string_view>
#include <tuple>
#include <utility>


namespace cruft {
    template <typename T>
    constexpr
    std::string_view type_name (void)
    {
        std::string_view pretty_function (__PRETTY_FUNCTION__);

#ifdef __clang__
        // PRETTY_FUNCTION = std::string_view cruft::type_name() [T = std::__1::vector<int, std::__1::allocator<int> >]

        std::string_view const prefix = "[T = ";
#elif defined(__GNUC__)
        // PRETTY_FUNCTION = "constexpr std::string_view cruft::type_name() [with T = std::__debug::vector<int>; std::string_view = std::basic_string_view<char>]"

        std::string_view prefix = "[with T = ";
#else
#error "Unsupported compiler"
#endif

        // Find the location where the type begins. It will also mark the start of
        // the type's namespace if the type has one.
        auto const ns_begin = std::search (
            pretty_function.begin (),
            pretty_function.end (),
            prefix.begin (),
            prefix.end ()
        );

        // Find the point the type name ends. Both use ']', but gcc lists
        // std::string_view too and so requires the delimiting ';' as a suffix.
        char const suffixes[] = ";]";
        auto const type_end = std::find_first_of (
            ns_begin,
            pretty_function.end (),
            std::begin (suffixes),
            std::end (suffixes)
        );

        // Find the start of the first template parameter (or the end of the
        // string otherwise), and the end of the template parameters for this
        // type.
        //
        // This cursor will be used to limit the scope of the namespace removal
        // we're about to do.
        auto const first_template = std::find (ns_begin, type_end, '<');
        auto const end_first_template = cruft::search::balanced (first_template, type_end, '<', '>');

        // Find the end of any namespace symbols
        auto const ns_symbol = std::find (
            std::make_reverse_iterator (first_template),
            std::make_reverse_iterator (ns_begin),
            ':'
        );

        // Compute the start of the symbol's type and return a view over this.
        auto const data = ns_symbol != std::make_reverse_iterator (ns_begin)
                          ? &*ns_symbol + 1
                          : ns_begin + prefix.size ();
        auto const size = std::distance (data, end_first_template);
        return std::string_view (data, size);
    }

    template <> constexpr std::string_view type_name<i08> (void) { return "i08"; }
    template <> constexpr std::string_view type_name<i16> (void) { return "i16"; }
    template <> constexpr std::string_view type_name<i32> (void) { return "i32"; }
    template <> constexpr std::string_view type_name<i64> (void) { return "i64"; }

    template <> constexpr std::string_view type_name<u08> (void) { return "u08"; }
    template <> constexpr std::string_view type_name<u16> (void) { return "u16"; }
    template <> constexpr std::string_view type_name<u32> (void) { return "u32"; }
    template <> constexpr std::string_view type_name<u64> (void) { return "u64"; }

    template <> constexpr std::string_view type_name<f32> (void) { return "f32"; }
    template <> constexpr std::string_view type_name<f64> (void) { return "f64"; }


    ///////////////////////////////////////////////////////////////////////////
    template <typename T>
    struct type_char;

    template <> struct type_char<float > { static constexpr char value = 'f'; };
    template <> struct type_char<double> { static constexpr char value = 'd'; };

    template <> struct type_char<  int8_t> { static constexpr char value = 'i'; };
    template <> struct type_char< int16_t> { static constexpr char value = 'i'; };
    template <> struct type_char< int32_t> { static constexpr char value = 'i'; };
    template <> struct type_char< int64_t> { static constexpr char value = 'i'; };

    template <> struct type_char< uint8_t> { static constexpr char value = 'u'; };
    template <> struct type_char<uint16_t> { static constexpr char value = 'u'; };
    template <> struct type_char<uint32_t> { static constexpr char value = 'u'; };
    template <> struct type_char<uint64_t> { static constexpr char value = 'u'; };

    template <typename T>
    constexpr auto type_char_v = type_char<T>::value;

    ///////////////////////////////////////////////////////////////////////////
    /// Lists valid values of an enumeration
    ///
    /// E: enumeration type
    ///
    /// Specialisations must provide the following constexpr:
    /// value_type:  typename
    /// value_count: size_t
    /// values:      static const std::array<value_type,value_count>
    template <
        typename E
    >
    struct enum_traits;

    ///////////////////////////////////////////////////////////////////////////
    /// Defines specialisations for introspection data structures for an
    /// enum E, in namespace NS, with variadic values __VA_ARGS__.
    ///
    /// Expects to be caleld from outside all namespaces.
    ///
    /// XXX: If we define the constexpr fields in a template specialised class
    /// clang has trouble instantiating them (with std=c++1z) resulting in
    /// undefined symbols at link time. By using a simple struct and inheriting
    /// from it we can avoid this problem. Revist this solution at clang-4.0.

    #define INTROSPECTION_ENUM_DECL(NS,E, ...)                          \
    namespace cruft {                                                   \
        struct PASTE(__enum_traits_,E) {                                \
            using value_type = ::NS::E;                                 \
                                                                        \
            static constexpr                                            \
            size_t value_count = VA_ARGS_COUNT(__VA_ARGS__);            \
                                                                        \
            static const                                                \
            std::array<value_type,value_count>                          \
            values;                                                     \
                                                                        \
            static const                                                \
            std::array<const char*,value_count>                         \
            names;                                                      \
        };                                                              \
                                                                        \
        template <>                                                     \
        struct enum_traits<::NS::E> : public PASTE(__enum_traits_,E)    \
        { };                                                            \
    }                                                                   \


    ///------------------------------------------------------------------------
    /// Declares specialisations for introspection data structures for an
    /// enum E, in namespace NS, with variadic values __VA_ARGS__.
    ///
    /// Expects to be called from outside all namespaces.
    #define INTROSPECTION_ENUM_IMPL(NS,E, ...)                  \
    const                                                       \
    std::array<                                                 \
        cruft::enum_traits<::NS::E>::value_type,                \
        cruft::enum_traits<::NS::E>::value_count                \
    > PASTE(cruft::__enum_traits_,E)::values = {                \
        MAP1(NAMESPACE_LIST, ::NS::E, __VA_ARGS__)              \
    };                                                          \
                                                                \
    const                                                       \
    std::array<                                                 \
        const char*,                                            \
        cruft::enum_traits<::NS::E>::value_count                \
    > PASTE(cruft::__enum_traits_,E)::names = {                 \
      MAP0(STRINGIZE_LIST, __VA_ARGS__)                         \
    };


    ///------------------------------------------------------------------------
    /// Defines an istream extraction operator for an enumeration E, within
    /// namespace NS
    ///
    /// Expects to be called from outside all namespaces.
    ///
    /// The user is responsible for specialising the ::cruft::enum_traits<NS::E>
    /// parameters which are used to drive the implementation (eg, through
    /// INTROSPECTION_ENUM_DECL, and INTROSPECTION_ENUM_IMPL).
    ///
    /// For trivial enumerations INTROSPECTION_ENUM may be easier to use.

    #define INTROSPECTION_ENUM_ISTREAM(NS,E)                    \
    std::istream&                                               \
    ::NS::operator>> (std::istream &is, ::NS::E &e)             \
    {                                                           \
        using traits = ::cruft::enum_traits<::NS::E>;           \
                                                                \
        std::string name;                                       \
        is >> name;                                             \
                                                                \
        std::transform (std::begin (name),                      \
                        std::end   (name),                      \
                        std::begin (name),                      \
                        ::toupper);                             \
                                                                \
        auto name_pos = std::find (                             \
            std::cbegin (traits::names),                        \
            std::cend   (traits::names),                        \
            name                                                \
        );                                                      \
                                                                \
        if (name_pos == std::cend (traits::names)) {            \
            is.setstate (std::istream::failbit);                \
        } else {                                                \
            auto d = std::distance (                            \
                std::begin (traits::names),                     \
                name_pos                                        \
            );                                                  \
                                                                \
            e = traits::values[d];                              \
        }                                                       \
                                                                \
        return is;                                              \
    }


    /// Defines an ostream insertion operator for an enumeration E, within
    /// namespace NS.
    ///
    /// Expects to be called from outside all namespaces.
    ///
    /// The user is responsible for specialising the ::cruft::enum_traits<NS::E>
    /// parameters which are used to drive the implementation (eg, through
    /// INTROSPECTION_ENUM_DECL, and INTROSPECTION_ENUM_IMPL).
    ///
    /// For trivial enumerations INTROSPECTION_ENUM may be easier to use.
    #define INTROSPECTION_ENUM_OSTREAM(NS,E)                    \
    std::ostream&                                               \
    ::NS::operator<< (std::ostream &os, ::NS::E e)              \
    {                                                           \
        using traits = ::cruft::enum_traits<::NS::E>;           \
                                                                \
        auto val_pos = std::find (                              \
            std::cbegin (traits::values),                       \
            std::cend   (traits::values),                       \
            e                                                   \
        );                                                      \
                                                                \
        if (val_pos == std::cend (traits::values)) {            \
            os.setstate (std::ostream::failbit);                \
        } else {                                                \
            auto d = std::distance (                            \
                std::cbegin (traits::values),                   \
                val_pos                                         \
            );                                                  \
                                                                \
            os << traits::names[d];                             \
        }                                                       \
                                                                \
        return os;                                              \
    }


    /// Defines an enum, its values, associated introspection structures, and
    /// istream and ostream operators.
    ///
    /// This must be called from outside all namespaces as
    /// INTROSPECTION_ENUM_DECL and INTROSPECTION_ENUM_IMPL need to declare
    /// and define structures outside the user's namespace.
    ///
    /// The enum will be defined inside an inline namespace to simplify the
    /// passing of parameters to functions which require some namespace
    /// prefixing. This shouldn't have a practical effect on user code.

    #define INTROSPECTION_ENUM(E, ...)                      \
    inline namespace detail_intr_enum {                     \
        enum E { __VA_ARGS__ };                             \
        std::ostream& operator<< (std::ostream&, E);        \
        std::istream& operator>> (std::istream&, E&);       \
    }                                                       \
    INTROSPECTION_ENUM_DECL(detail_intr_enum,E,__VA_ARGS__) \
    INTROSPECTION_ENUM_IMPL(detail_intr_enum,E,__VA_ARGS__) \
    INTROSPECTION_ENUM_ISTREAM(detail_intr_enum,E)          \
    INTROSPECTION_ENUM_OSTREAM(detail_intr_enum,E)


    #define INTROSPECTION_ENUM_CLASS(E, ...)                \
    inline namespace detail_intr_enum {                     \
        enum class E { __VA_ARGS__ };                       \
        std::ostream& operator<< (std::ostream&, E);        \
        std::istream& operator>> (std::istream&, E&);       \
    }                                                       \
    INTROSPECTION_ENUM_DECL(detail_intr_enum,E,__VA_ARGS__) \
    INTROSPECTION_ENUM_IMPL(detail_intr_enum,E,__VA_ARGS__) \
    INTROSPECTION_ENUM_ISTREAM(detail_intr_enum,E)          \
    INTROSPECTION_ENUM_OSTREAM(detail_intr_enum,E)


    ///////////////////////////////////////////////////////////////////////////
    /// Describes a single member variable in a type availabe for introspection
    ///
    /// K: target class
    /// R: member type
    /// M: pointer-to-member
    template <
        class K,
        typename R,
        R K::*M
    >
    struct field
    {
        typedef K klass;
        typedef R type;

        static const std::string name;

        static const R& get (const K &k) { return k.*M; }
        static       R& get (      K &k) { return k.*M; }
        static       R& get (      K &&) = delete;
    };

    ///////////////////////////////////////////////////////////////////////////
    /// Holds the fields of a type available for introspection
    ///
    /// Specialise the following type struct with a 'fields' tuple of the
    /// members that should be accessed like below:
    ///
    /// struct foo { int a; int b; };
    ///
    /// template <> struct type<foo>
    /// {
    ///     typedef std::tuple<
    ///         field<foo,int,&foo::a>,
    ///         field<foo,int,&foo::b>
    ///     > fields;
    /// };
    ///
    /// template <> const std::string field<foo,int,&foo::a>::name = "a";
    /// template <> const std::string field<foo,int,&foo::b>::name = "b";

    template <class K>
    struct type { };


    ///////////////////////////////////////////////////////////////////////////
    /// traits class which converts an introspected type to a tuple
    ///
    /// K: target class

    template <typename K>
    struct type_tuple;

    template <
        typename ...T
    > struct type_tuple<
        std::tuple<T...>
    > {
        typedef std::tuple<T...> type;
    };


    template <
        typename K,
        typename I = typename std::make_index_sequence<
            std::tuple_size<
                typename type<K>::fields
            >::value
        >
    > struct _type_tuple;

    template <
        typename K,
        size_t ...I
    > struct _type_tuple <
        K,
        std::index_sequence<I...>
    > {
        typedef std::tuple<
            typename std::tuple_element<
                I,
                typename type<K>::fields
            >::type::type...
        > type;
    };


    template <
        typename K
    > struct type_tuple {
        typedef typename _type_tuple<K>::type type;
    };


    ///////////////////////////////////////////////////////////////////////////
    namespace detail {
        template <
            typename K,
            typename I = typename std::make_index_sequence<
                std::tuple_size<
                    typename type<K>::fields
                >::value
            >
        >
        struct _as_tuple;

        template <
            typename K,
            size_t ...I
        >
        struct _as_tuple <
            K,
            std::index_sequence<I...>
        >
        {
            static typename type_tuple<K>::type
            make (const K &k)
            {
                return std::make_tuple (
                    std::tuple_element<I, typename type<K>::fields>::type::get (k)...
                );
            }

            static auto make (K&&) = delete;
        };
    }

    /// Convert an introspection capable class instance into a tuple instance
    ///
    /// K: source class
    template <typename K>
    auto
    as_tuple (const K &k)
    {
        return detail::_as_tuple<K>::make (k);
    }

    template <typename K>
    auto as_tuple (K &_k)
    {
        const K &k = _k;
        return as_tuple (k);
    }

    template <typename K>
    auto as_tuple (K&&) = delete;
}