Re: [boost] [mpl] bug: mpl::is_sequence< mpl::int_<1> > fails to compile

From: David Abrahams (dave_at_[hidden])
Date: 2006-05-07 17:50:40

Tobias Schwinger <tschwinger_at_[hidden]> writes:

> David Abrahams wrote:
>> Tobias Schwinger <tschwinger_at_[hidden]> writes:
>> 
>> 
>>>For those about to reply "don't use is_sequence" please answer this
>>>question first:
>>>
>>>How to traverse a tree where the nodes are sequences and the leafes
>>>are mpl::intS without it?
>> 
>> 
>> Just reformulate the tree so that nodes are all wrapped in something
>> you can recognize reliably:
>> 
>>      tree<
>>          list<
>>              tree<vector<int, long> >
>>            , tree<vector<long,int> >
>>          >
>>      >
>> 
>
> Pretty nice for hard-wired input -- impractical in my case, though. 
> Why not make is_sequence work reliably? 

Because it's impossible.  It's always going to look for some features
of the type being tested that can be present even if the type is not,
in fact, a sequence.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com