[boost] Am I missing something or is Boost: String dictionary?

Subject: [boost] Am I missing something or is Boost: String dictionary?
From: david.hagood_at_[hidden]
Date: 2013-05-06 11:26:46

One of the libraries I work with (libXML2) has a very useful concept
called a string dictionary, and I am surprised this doesn't appear to be
in either STL or Boost. Am I missing something, or is Boost missing
something?

The basic idea is:
Given you have a string and an instance of a dictionary, you can:
1) check if the string is already in the dictionary.
2) Add the string to the dictionary and return the dictionary entry (if
the string is already present, return existing entry).

The dictionary entries contain a copy of the string. Entries may be
compared for equality/inequality in O(1) time. The lifespan of the strings
in the entry is managed by the entry.

This really simplifies writing parsers and the like, and is such a useful
concept that I'm really surprised not to see it in STL or Boost.