rippled/include/xrpl/beast/core/LexicalCast.h

#ifndef BEAST_MODULE_CORE_TEXT_LEXICALCAST_H_INCLUDED
#define BEAST_MODULE_CORE_TEXT_LEXICALCAST_H_INCLUDED

#include <xrpl/beast/utility/instrumentation.h>

#include <boost/core/detail/string_view.hpp>

#include <algorithm>
#include <cerrno>
#include <charconv>
#include <cstdlib>
#include <iterator>
#include <string>
#include <type_traits>
#include <typeinfo>

namespace beast {

namespace detail {

// These specializatons get called by the non-member functions to do the work
template <class Out, class In>
struct LexicalCast;

// conversion to std::string
template <class In>
struct LexicalCast<std::string, In>
{
    explicit LexicalCast() = default;

    template <class Arithmetic = In>
    std::enable_if_t<std::is_arithmetic_v<Arithmetic>, bool>
    operator()(std::string& out, Arithmetic in)
    {
        out = std::to_string(in);
        return true;
    }

    template <class Enumeration = In>
    std::enable_if_t<std::is_enum_v<Enumeration>, bool>
    operator()(std::string& out, Enumeration in)
    {
        out = std::to_string(
            static_cast<std::underlying_type_t<Enumeration>>(in));
        return true;
    }
};

// Parse a std::string_view into a number
template <typename Out>
struct LexicalCast<Out, std::string_view>
{
    explicit LexicalCast() = default;

    static_assert(
        std::is_integral_v<Out>,
        "beast::LexicalCast can only be used with integral types");

    template <class Integral = Out>
    std::enable_if_t<
        std::is_integral_v<Integral> && !std::is_same_v<Integral, bool>,
        bool>
    operator()(Integral& out, std::string_view in) const
    {
        auto first = in.data();
        auto last = in.data() + in.size();

        if (first != last && *first == '+')
            ++first;

        auto ret = std::from_chars(first, last, out);

        return ret.ec == std::errc() && ret.ptr == last;
    }

    bool
    operator()(bool& out, std::string_view in) const
    {
        std::string result;

        // Convert the input to lowercase
        std::transform(
            in.begin(), in.end(), std::back_inserter(result), [](auto c) {
                return std::tolower(static_cast<unsigned char>(c));
            });

        if (result == "1" || result == "true")
        {
            out = true;
            return true;
        }

        if (result == "0" || result == "false")
        {
            out = false;
            return true;
        }

        return false;
    }
};
//------------------------------------------------------------------------------

// Parse boost library's string_view to number or boolean value
// Note: As of Jan 2024, Boost contains three different types of string_view
// (boost::core::basic_string_view<char>, boost::string_ref and
// boost::string_view). The below template specialization is included because
// it is used in the handshake.cpp file
template <class Out>
struct LexicalCast<Out, boost::core::basic_string_view<char>>
{
    explicit LexicalCast() = default;

    bool
    operator()(Out& out, boost::core::basic_string_view<char> in) const
    {
        return LexicalCast<Out, std::string_view>()(out, in);
    }
};

// Parse std::string to number or boolean value
template <class Out>
struct LexicalCast<Out, std::string>
{
    explicit LexicalCast() = default;

    bool
    operator()(Out& out, std::string in) const
    {
        return LexicalCast<Out, std::string_view>()(out, in);
    }
};

// Conversion from null terminated char const*
template <class Out>
struct LexicalCast<Out, char const*>
{
    explicit LexicalCast() = default;

    bool
    operator()(Out& out, char const* in) const
    {
        XRPL_ASSERT(
            in, "beast::detail::LexicalCast(char const*) : non-null input");
        return LexicalCast<Out, std::string_view>()(out, in);
    }
};

// Conversion from null terminated char*
// The string is not modified.
template <class Out>
struct LexicalCast<Out, char*>
{
    explicit LexicalCast() = default;

    bool
    operator()(Out& out, char* in) const
    {
        XRPL_ASSERT(in, "beast::detail::LexicalCast(char*) : non-null input");
        return LexicalCast<Out, std::string_view>()(out, in);
    }
};

}  // namespace detail

//------------------------------------------------------------------------------

/** Thrown when a conversion is not possible with LexicalCast.
    Only used in the throw variants of lexicalCast.
*/
struct BadLexicalCast : public std::bad_cast
{
    explicit BadLexicalCast() = default;
};

/** Intelligently convert from one type to another.
    @return `false` if there was a parsing or range error
*/
template <class Out, class In>
bool
lexicalCastChecked(Out& out, In in)
{
    return detail::LexicalCast<Out, In>()(out, in);
}

/** Convert from one type to another, throw on error

    An exception of type BadLexicalCast is thrown if the conversion fails.

    @return The new type.
*/
template <class Out, class In>
Out
lexicalCastThrow(In in)
{
    if (Out out; lexicalCastChecked(out, in))
        return out;

    throw BadLexicalCast();
}

/** Convert from one type to another.

    @param defaultValue The value returned if parsing fails
    @return The new type.
*/
template <class Out, class In>
Out
lexicalCast(In in, Out defaultValue = Out())
{
    if (Out out; lexicalCastChecked(out, in))
        return out;

    return defaultValue;
}

}  // namespace beast

#endif