 key must be convertible to a value of the
map's key type. Details of that conversion are unspecified.
2) For this expression to be valid, the key must be
associated with some value, otherwise the result is undefined.</p>
<pre class="literal-block">
std::string get_string(const any&amp; key)
</pre>
<p>Given a representation of a key, return the string representation
of the value associated with that key.</p>
<p>Requirements:
1) The object passed as the key must be convertible to the
property map's key type.