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From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2005-03-03 19:20:22

David Abrahams wrote:
> Tobias Schwinger <tschwinger_at_[hidden]> writes:
>>This code:
>>#include <boost/mpl/vector.hpp>
>>#include <boost/mpl/pop_front.hpp>
>>#include <boost/mpl/assert.hpp>
>>#include <boost/mpl/equal.hpp>
>>using namespace boost;
>>// Doc says: pop_front returns a vector
>>typedef mpl::pop_front< mpl::vector<bool,char,int> >::type v;
>>// Doc says: vectors have a type member equal to itself
>> mpl::equal< v, v::type >
>>fails to compile with GCC ( v::type is mpl::vector3<bool,char,int> )
> That's a bug. If that's truly happening, the documentation is correct
> and the implementation is wrong.

Here's the output of the above program in case you don't have a gcc
handy to convince yourself:

tmp.cpp:12: error: conversion from
`mpl_::failed************boost::mpl::equal<v, boost::mpl::vector3<bool,
char, int>, boost::is_same<mpl_::_, mpl_::_> >::************' to
non-scalar type `mpl_::assert< false>' requested
tmp.cpp:12: error: enumerator value for `mpl_assertion_in_line_14' not
integer constant

> No, it should be fixed.
> mpl::pop_front< mpl::vector<bool,char,int> >::type::type
> should always be a sequence of length 2 containing (char, int).

Problems resulting from this are for sure vicious to track...

Note that 'pop_front' is arbitrary - it applies to all front/back mutators.



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