For fun: Expressive C++ 17 Coding Challenge in D

[Biotronic]

On Wednesday, 4 October 2017 at 09:04:58 UTC, Biotronic wrote:
> Since the code uses ranges though, a simple replacement of 
> readText with an mmapped equivalent should enable humongous 
> file support with no other code change required.

Drop-in replacement for readText:

struct MmText {
     import std.mmfile;

     ulong  _fileOffset;
     MmFile _file;

     this(string filename) {
         _file = new MmFile(filename);
     }

     dchar front() {
         auto end = min(_file.length, _fileOffset+4);
         auto data = cast(string)_file[_fileOffset..end];
         return decodeFront(data);
     }

     void popFront() {
         auto end = min(_file.length, _fileOffset+4);
         auto data = cast(string)_file[_fileOffset..end];
         size_t bytes;
         decodeFront(data, bytes);
         _fileOffset += bytes;
     }

     bool empty() {
         return _fileOffset >= _file.length;
     }
}

--
   Biotronic