Symbolic member names

From: Greg Chicares (chicares_at_[hidden])
Date: 2001-08-26 19:49:11

Given

  struct S
  { int i0; int i1; double d0; std::string s0;};

I would like to be able to write

  S s;
  s["i0"] = "999.9"; // truncates to int
  s["i1"] = "888e3"; // converts to int
  s["d0"] = "777";   // converts to double
  s["s0"] = "hello";

such that

  std::cout << s.i0 << " " << s.i1 << " "
            << s.d0 << " " << s.s0 << "\n";

returns

  999 888000 777 hello

This can be done by adding a symbol table to 'S' and
'ascribing' each member to the symbol table in the ctor:

  struct S : public MemberSymbolTable<S>
  {
    int i0; int i1; double d0; std::string s0;
    S() : i0(0), i1(0), d0(0.0)
      {
      ascribe("i0", &S::i0);
      ascribe("i1", &S::i1);
      ascribe("d0", &S::d0);
      ascribe("s0", &S::s0);
      }
  };

I find this useful e.g. for cgi-bin where potentially many
name-value pairs like
  {"i0", 123}
would otherwise need to be treated as
  s.i0 = lexical_cast<int>    (GetValue(cgi_data, "i0"));
  s.d0 = lexical_cast<double> (GetValue(cgi_data, "d0"));
and yet a strongly-typed struct is wanted downstream instead
of a heterogeneous property map.

That was my original motivation, but there are other uses
as well. For instance, sometimes I need to calculate a CRC
of all members of a struct, and this makes it easier than
writing CRC(s.i0) + CRC(s.i1) + ... .

Is anyone interested in seeing the implementation?