On Sat, 24 Mar 2012, Michel Morin wrote:

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Author: jewillco Date: 2012-03-23 15:35:52 EDT (Fri, 23 Mar 2012) New Revision: 77506 URL: http://svn.boost.org/trac/boost/changeset/77506 […] --- (empty file) +++ trunk/boost/property_map/function_property_map.hpp  2012-03-23 […] +#ifndef BOOST_PROPERTY_MAP_FUNCTION_PROPERTY_MAP_H +#define BOOST_PROPERTY_MAP_FUNCTION_PROPERTY_MAP_H […] +#endif /* BOOST_PROPERTY_MAP_FUNCTION_PROPERTY_MAP_H */

s/H/HPP

I've fixed that.

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+template<typename Func, typename Key, typename Ret = typename boost::result_of<Func(Key)>::type> +class function_property_map: public put_get_helper<Ret, function_property_map<Func, Key, Ret> > { […] +  typedef Ret reference; […] +  reference operator[](const Key& k) const { +    return f(k); +  } + +  reference operator[](const Key& k) { +    return f(k); +  } […] +  private: +  Func f; +};

In const version of the subscript operator, `f` is treated as `const Func`. So `reference` might not be appropriate for its return type. You can avoid this issue by making `f` mutable.

Or, how about defining the default template argument of `Ret` as `boost::result_of<const Func(Key)>::type` and removing non-const version of the subscript operator? (Since property maps are often passed around by values, it makes less sense to allow stateful functors in `function_property_map`, IMHO.)

I did the second approach you mentioned. Please check r77514 and see if you like how I've incorporated your suggestions. Thank you for your comments. -- Jeremiah Willcock