string_view.hpp

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// Copyright (C) 2020-2024 Jonathan Müller and lexy contributors
// SPDX-License-Identifier: BSL-1.0
 
#ifndef LEXY_DETAIL_STRING_VIEW_HPP_INCLUDED
#define LEXY_DETAIL_STRING_VIEW_HPP_INCLUDED
 
#include <lexy/_detail/assert.hpp>
#include <lexy/_detail/config.hpp>
#include <lexy/_detail/integer_sequence.hpp>
 
namespace lexy::_detail
{
struct null_terminated
{};
 
template <typename CharT>
class basic_string_view
{
    static constexpr CharT empty_string[] = {CharT()};
 
public:
    using char_type = CharT;
 
    //=== constructor ===//
    constexpr basic_string_view() noexcept : _ptr(empty_string), _size(0u), _null_terminated(true)
    {}
 
    constexpr basic_string_view(const char_type* str) noexcept
    : _ptr(str), _size(0u), _null_terminated(true)
    {
        while (*str++)
            ++_size;
    }
 
    constexpr basic_string_view(const char_type* ptr, std::size_t size) noexcept
    : _ptr(ptr), _size(size), _null_terminated(false)
    {}
    constexpr basic_string_view(null_terminated, const char_type* ptr, std::size_t size) noexcept
    : _ptr(ptr), _size(size), _null_terminated(true)
    {
        LEXY_PRECONDITION(_ptr[_size] == CharT());
    }
 
    constexpr basic_string_view(const char_type* begin, const char_type* end) noexcept
    : _ptr(begin), _size(std::size_t(end - begin)), _null_terminated(false)
    {
        LEXY_PRECONDITION(begin <= end);
    }
 
    //=== access ===//
    using iterator = const char_type*;
 
    constexpr iterator begin() const noexcept
    {
        return _ptr;
    }
    constexpr iterator end() const noexcept
    {
        return _ptr + _size;
    }
 
    constexpr bool empty() const noexcept
    {
        return _size == 0u;
    }
    constexpr std::size_t size() const noexcept
    {
        return _size;
    }
    constexpr std::size_t length() const noexcept
    {
        return _size;
    }
 
    constexpr char_type operator[](std::size_t i) const noexcept
    {
        LEXY_PRECONDITION(i <= _size);
        return _ptr[i];
    }
    constexpr char_type front() const noexcept
    {
        LEXY_PRECONDITION(!empty());
        return *_ptr;
    }
    constexpr char_type back() const noexcept
    {
        LEXY_PRECONDITION(!empty());
        return _ptr[_size - 1];
    }
 
    constexpr const char_type* data() const noexcept
    {
        return _ptr;
    }
 
    constexpr bool is_null_terminated() const noexcept
    {
        return _null_terminated;
    }
 
    constexpr const char_type* c_str() const noexcept
    {
        LEXY_PRECONDITION(is_null_terminated());
        return _ptr;
    }
 
    //=== operations ===//
    static constexpr std::size_t npos = std::size_t(-1);
 
    constexpr void remove_prefix(std::size_t n) noexcept
    {
        LEXY_PRECONDITION(n <= _size);
        _ptr += n;
        _size -= n;
    }
    constexpr void remove_suffix(std::size_t n) noexcept
    {
        LEXY_PRECONDITION(n <= _size);
        _size -= n;
        _null_terminated = false;
    }
 
    constexpr basic_string_view substr(std::size_t pos, std::size_t length = npos) const noexcept
    {
        LEXY_PRECONDITION(pos < _size);
        if (length >= _size - pos)
        {
            auto result             = basic_string_view(_ptr + pos, end());
            result._null_terminated = _null_terminated;
            return result;
        }
        else
        {
            // Note that we're loosing null-terminated-ness.
            return basic_string_view(_ptr + pos, length);
        }
    }
 
    constexpr bool starts_with(basic_string_view prefix) const noexcept
    {
        return substr(0, prefix.size()) == prefix;
    }
    constexpr bool try_remove_prefix(basic_string_view prefix) noexcept
    {
        if (!starts_with(prefix))
            return false;
 
        remove_prefix(prefix.length());
        return true;
    }
 
    constexpr std::size_t find(basic_string_view str, std::size_t pos = 0) const noexcept
    {
        for (auto i = pos; i < length(); ++i)
        {
            if (substr(i, str.length()) == str)
                return i;
        }
 
        return npos;
    }
    constexpr std::size_t find(CharT c, std::size_t pos = 0) const noexcept
    {
        return find(basic_string_view(&c, 1), pos);
    }
 
    //=== comparison ===//
    friend constexpr bool operator==(basic_string_view<CharT> lhs,
                                     basic_string_view<CharT> rhs) noexcept
    {
        if (lhs.size() != rhs.size())
            return false;
 
        for (auto a = lhs.begin(), b = rhs.begin(); a != lhs.end(); ++a, ++b)
            if (*a != *b)
                return false;
 
        return true;
    }
 
    friend constexpr bool operator!=(basic_string_view<CharT> lhs,
                                     basic_string_view<CharT> rhs) noexcept
    {
        return !(lhs == rhs);
    }
 
private:
    const CharT* _ptr;
    std::size_t  _size;
    bool         _null_terminated;
};
using string_view = basic_string_view<char>;
} // namespace lexy::_detail
 
namespace lexy::_detail
{
template <auto FnPtr, typename Indices = make_index_sequence<FnPtr().size()>>
struct _string_view_holder;
template <auto FnPtr, std::size_t... Indices>
struct _string_view_holder<FnPtr, index_sequence<Indices...>>
{
    static constexpr auto view = FnPtr();
 
    static constexpr typename decltype(view)::char_type value[] = {view[Indices]..., {}};
};
 
template <auto FnPtr>
inline constexpr const auto* make_cstr = _string_view_holder<FnPtr>::value;
} // namespace lexy::_detail
 
#endif // LEXY_DETAIL_STRING_VIEW_HPP_INCLUDED