Re: [Boost-users] [boost] [mpl] Hard upper limit for range_c

Subject: Re: [Boost-users] [boost] [mpl] Hard upper limit for range_c
From: Larry Evans (cppljevans_at_[hidden])
Date: 2014-05-13 14:03:32

On 05/13/14 11:23, Javier Dehesa wrote:> I was testing for_each and 
range_c and I've discovered that there's a
 > hard limit in the range_c template.
 >
 > I'm attaching an example (copied from the for_each docs
 > 
http://www.boost.org/doc/libs/1_55_0/libs/mpl/doc/refmanual/for-each.html)
 > to illustrate it. This program compiles fine for me (g++ 4.9.0), but if
 > I set NUM to a number over 890, the compilation fails. I receive an
 > error about template instantiation depth, so I guess I could tune it in
 > the compiler to make it work. But, anyway, why is this template
 > recursively defined? Is it on purpose?

On purpose:

http://www.boost.org/doc/libs/1_31_0/libs/mpl/doc/paper/mpl_paper.html

The reason for only using recursion is that an imperative like loop:

   std::vector<int> int_list;
   for(unsigned i=0; i<890; ++i) int_list.push_back(i);

the value of i and int_list are modified during each iteration of the
loop.  TMP is a pure *functional* language, meaning there is no
changing of the value of a variable.  Once it's calculated, the value
cannot be changed.

HTH.

-regards,
Larry