[RFC/partial patch] libstdc++/11400

[Paolo Carlini]

Hi,

this is the testcase:

//////

#include <algorithm>

struct Integral { operator int() const; };

namespace std {

template int* search_n (int*, int*, Integral, const int&);

}

//////

which currently doesn't compile

/build/contrib/gcc-3.2/include/c++/3.2/bits/stl_algo.h: In function 
   `_ForwardIter std::search_n(_ForwardIter, _ForwardIter, _Integer, const 
   _Tp&) [with _ForwardIter = int*, _Integer = Integral, _Tp = int]':
t.cpp:7:   instantiated from here
/build/contrib/gcc-3.2/include/c++/3.2/bits/stl_algo.h:612: conversion from `
   int' to non-scalar type `Integral' requested
/build/contrib/gcc-3.2/include/c++/3.2/bits/stl_algo.h:617: no match for `-- 
   Integral&' operator

what I'm proposing is dispatching basing on the _Is_integer trait to a general
safe version using distance() and a special version same as the current one.

I'm attaching below a *preliminary* patch for the first of the two versions
of search_n, the simplest, that without the BinaryPredicate.

Seems a reasonable approach? In case I would complete it with the second case,
prepare a set of testcases, missing for search_n, and so on...

Paolo.

//////////

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