Re: Perl style hash

James Kanze <>
Thu, 10 Sep 2009 03:42:42 -0700 (PDT)
On Sep 10, 12:22 am, Sam <> wrote:

none writes:

I'm sure something similar could be done in C++, probably
using a wrapper around std::map that provided operator
overloading for maybe the [] operator, and I guess you'd
need to overload the = operator to accept any type of data
that you might want to store in a leaf.

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).

If you're using operator[] on std::map, the mapped type must
also support default construction.

It's all a matter of implementing the two classes, with the
appropriate semantics. All you need to do is define a value
class that implements operator[] using your desired semantics.

The important thing here is that the mapped type (but not the
key type) of a map can itself be a map, so you can have
something like:
    std::map< Key1, std::map< Key2, std::map< Key3, Mapped > > >

The other important point is that it is NOT a hash table; if
this is important (e.g. millions of entries), there is an
unsorted_map in TR1, and in the next version of the standard,
which will be a hash table.

James Kanze

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