Re: [boost] If boost::fusion is the hammer, then what's the nail?

From: Joel de Guzman (joel_at_[hidden])
Date: 2006-12-14 17:55:32

Larry Evans wrote:
> On 12/14/2006 08:52 AM, Thorsten Ottosen wrote:
> [snip]
>> I have used tuples in a similar manner, but I kinda think its not the 
>> best to do; a named tuple would be more appropriate, or maybe just a struct.
>>
>> What bothers me is the self-explanatory properties are lost; I can't 
>> figure out what tuple element that means what by just looking at the 
>> code. Is it
>>
>>    tie(eval,dev1,dev2) = find_root(...)
>>
>> or
>>
>>    tie(dev1,dev2,eval) = find_root(...)
>>
>> ?
>>
> This "named tuple" is essentially the composite_product whose test
> code is here:
> 
> http://boost.cvs.sourceforge.net/boost-sandbox/boost-sandbox/libs/indexed_types/test/composite_product_test.cpp
> 
> Instead of field names, numerators in an enumeration are used.  For 
> example, in the above test, the numerators, {a,b,c} of the enumeration, 
> indices, correspond to the field names in the following struct:
> 
>    struct
> r_struct
> {
>      field_ndx<a> a_field;
>      field_ndx<b> b_field;
>      field_ndx<c> c_field;
> };

Looks very similar to the fusion map except for the use of enum
tags. Enums are not good as tags because you have to close them;
they are not open to extension.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net