std.mmfile.MmFile does not contain opDollar, so when trying to access the .length property, you get an error. E.g:
import std.stdio, std.mmfile;
void main() {
MmFile shar = new MmFile(null, MmFile.Mode.readWrite, 10, null, 0);
string output = shar[0 .. $];
}
Would error due to "undefined identifier __dollar"