Re: [Boost-users] Understanding Boost.Mpl Fold Algorithm

Hi Dave, Re-reading this great book for the 2nd time, and studying chapter 11 I found myself trying to understand the mpl::fold algorithm. Thanks for this wonderful work. My best regards, Eduardo On 1/8/06, David Abrahams wrote:

Eduardo Bezerra writes:

...

Hi,

I'm having a hard time trying to understand what the placeholders _1 and _2 mean in the context of the mpl::fold algorithm.

...

From the Boost.Mpl Reference manual:

typedef vector types;

typedef fold< types , int_<0> , if_< is_float<_2>,next<_1>,_1 >

...

::type number_of_floats;

BOOST_MPL_ASSERT_RELATION( number_of_floats::value, ==, 4 );

Could someone give me some help on this ?

<shameless plug> http://www.boost-consulting.com/mplbook contains a good explanation.

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

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