Re: [boost] [Boost-commit] svn:boost r77506 - in trunk: boost/property_map libs/property_map/doc libs/property_map/test

Subject: Re: [boost] [Boost-commit] svn:boost r77506 - in trunk: boost/property_map libs/property_map/doc libs/property_map/test
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2012-03-24 13:31:01

On Sat, 24 Mar 2012, Michel Morin wrote:

>> 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.

>> +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