fast_istreambuf_iterator.hpp

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// -----------------------------------------------------------------------------------------------------
// Copyright (c) 2006-2021, Knut Reinert & Freie Universität Berlin
// Copyright (c) 2016-2021, Knut Reinert & MPI für molekulare Genetik
// This file may be used, modified and/or redistributed under the terms of the 3-clause BSD-License
// shipped with this file and also available at: https://github.com/seqan/seqan3/blob/master/LICENSE.md
// -----------------------------------------------------------------------------------------------------
 
#pragma once
 
#include <cassert>
#include <seqan3/std/iterator>
 
#include <seqan3/io/stream/detail/stream_buffer_exposer.hpp>
 
namespace seqan3::detail
{
template <typename char_t, typename traits_t = std::char_traits<char_t>>
class fast_istreambuf_iterator
{
private:
    stream_buffer_exposer<char_t, traits_t> * stream_buf = nullptr;
 
public:
    using difference_type   = ptrdiff_t;               
    using value_type        = char_t;                  
    using reference         = char_t;                  
    using pointer           = void;                    
    using iterator_category = std::input_iterator_tag; 
 
    fast_istreambuf_iterator()                                              noexcept = default; 
    fast_istreambuf_iterator(fast_istreambuf_iterator const &)              noexcept = default; 
    fast_istreambuf_iterator(fast_istreambuf_iterator &&)                   noexcept = default; 
    fast_istreambuf_iterator & operator=(fast_istreambuf_iterator const &)  noexcept = default; 
    fast_istreambuf_iterator & operator=(fast_istreambuf_iterator &&)       noexcept = default; 
    ~fast_istreambuf_iterator()                                             noexcept = default; 
 
    explicit fast_istreambuf_iterator(std::basic_streambuf<char_t, traits_t> & ibuf) :
        stream_buf{reinterpret_cast<stream_buffer_exposer<char_t, traits_t> *>(&ibuf)}
    {
        assert(stream_buf != nullptr);
        stream_buf->underflow(); // ensure the stream buffer has content on construction
    }
 
    fast_istreambuf_iterator & operator++()
    {
        assert(stream_buf != nullptr);
        if ((stream_buf->gptr() + 1) == stream_buf->egptr())
            stream_buf->snextc(); // move right, then underflow()
        else
            stream_buf->gbump(1);
        return *this;
    }
 
    void operator++(int)
    {
        ++(*this);
    }
 
    reference operator*() const
    {
        assert(stream_buf != nullptr);
        return *stream_buf->gptr();
    }
 
    friend bool operator==(fast_istreambuf_iterator const & lhs, std::default_sentinel_t const &) noexcept
    {
        assert(lhs.stream_buf != nullptr);
        // compare size of remaining buffer; since ++ always resizes if possible, safe to compare pointers here
        return (lhs.stream_buf->gptr() == lhs.stream_buf->egptr());
    }
 
    friend bool operator!=(fast_istreambuf_iterator const & lhs, std::default_sentinel_t const &) noexcept
    {
        return !(lhs == std::default_sentinel);
    }
 
    friend bool operator==(std::default_sentinel_t const &, fast_istreambuf_iterator const & rhs) noexcept
    {
        return rhs == std::default_sentinel;
    }
 
    friend bool operator!=(std::default_sentinel_t const &, fast_istreambuf_iterator const & rhs) noexcept
    {
        return !(rhs == std::default_sentinel);
    }
};
 
} // namespace seqan3::detail