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Subject: Re: [Boost-users] mpl/fusion: metafunction to 'rangify'
From: Hicham Mouline (hicham_at_[hidden])
Date: 2009-12-23 15:13:01

>> typedef 
>> boost::fusion::result_of::as_vector<boost::fusion::result_of::transform< 
>> params,make_fixed_or_range>::type>::type 
>> params_fixed_or_range; 
>> -Christopher 
>It does. 
>Of course, the return type of fusion::transform contains the compile-time 
>information required. 
>Thanks very much, 
>Now I'll look at spirit (and some magic code to generate the Qi parser for 
>this new sequence) to fill it up with values from an input stream. 

I have simplified the code to

I have a couple of needs now:

1. attempt to transform pfr back to params. This should succeed if all
elements of the fusion sequence are fixed values and throw an exception if
any of them is a range. Should I write this as a free floating function, as
a conversion operator?

2. there will be many params types, params_1 .... params_n, each of those
structs will yield after a fusion::transform the sequences
params_fixed_of_range_1... params_fixed_of_range_n.
I need the following behavior (I would write for this a free floating
template function, templated on the sequence type : one of the

template <typename params_fixed_of_range>
void do_work(const params_fixed_of_range& seq_i) {
  /// generate a inner for loop for all the ranges in seq_i
  /// for e.g., if seq_i contains
  /// { d1= 5.; d2= 4.0..5.0..0.1; d3=-1.5..1.5..0.6; i4=4..26..1;
i5=4; i6=0; i7=0; }
  /// then I would want to generate the following code, or if impossible
  /// maybe by runtime recursion
  for (double d2=4.0; d2<=5.0; d2+=0.1)
    for (double d3=-1.5; d3<=1.5; d3+=0.6)
      for (unsigned int i4=4; i4<=26; i4+=1)
         // I know d1=5. i5=4 i6=0 i7=0
         // construct a params frm current d1,d2,d3,i4,i5,i6,i7
         // do some work based on params
         // return value, this will be used to plot graphs

This seems very doable with boost.fusion, and extremely complicated and not
flexible without it.

I realize there are a lot of questions into 1 email but appreciate the help
you can give me,

Best regards,

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