Re: Perl style hash

James Kanze <>
Thu, 10 Sep 2009 03:48:01 -0700 (PDT)
On Sep 10, 2:14 am, none <n...@none.none> wrote:

Sam wrote:

No need to overload anything. Both the key or the value in a
std::map can be any class, with the only restriction that
the key class must implement operator<() (ignoring the
hair-splitting requirement for the implementation of copy
constructors and assignment operators).

Sure, but the type of the elements are determined at compile
time. In other words, you can't just do this:

   std::map<std::string, Anything> x;

   x["a float"] = 5.0f;
   x["an int"] = 10;
   x["a string"] = "some text";

You can; just map to boost::any (although I'm not too sure what
boost::any would do with a string literal). Except in unusual
cases, however, it's something to avoid; the fact that perl
doesn't have any real typing is a definite defect in the
language, at least if you want to use it for larger programs.

And even if you could, you still wouldn't have the perl-style
behavior that I described. If you tried:

   x["root"]["branch"]["leaf"] = 5;

the compiler would not know how to resolve the second (and
third) set of braces.

You could probably define an Any class yourself which would.
Whether it's a good idea or not is another question.

James Kanze

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