Hi,
could please somebody tell me why the code below generates a compile-time
error?
The compiler I'm using is VC++ 7.1.
The error generated is this:
c:\Program Files\Microsoft Visual Studio .NET
2003\Vc7\include\algorithm(458) : error C2582: 'operator =' function is
unavailable in 'item_proxy'
c:\PROG\VCPP\xItFacadeReferProxy\xItFacadeReferProxy.cpp(102) :
see reference to function template instantiation 'void
std::generate(_FwdIt,_FwdIt,_Fn0)'
being compiled
with
[
_FwdIt=Array_iterator,
_Fn0=int (__cdecl *)(void)
]
the location of the error in <algorithm>:
template inline
void generate(_FwdIt _First, _FwdIt _Last, _Fn0 _Func)
{ // replace [_First, _Last) with _Func()
for (; _First != _Last; ++_First)
*_First = _Func(); // ERROR HERE
}
To my best knowledge, item_proxy's operator= is public, so I don't
understand why it is unavailable.
Thx,
Gus
The code:
------------------------------------------------------------------------
// xItFacadeReferProxy.cpp : Defines the entry point
// for the console application.
#include "stdafx.h"
#include <algorithm>
#include
using namespace boost;
using namespace std;
// THIS CLASS IS GOING TO BE 'STL'IZED':
const int ARRAY_SIZE = 10;
class Array {
public:
int Get(int i) const { return data[i]; }
int Set(int i, int val) { data[i] = val; }
private:
int data[ARRAY_SIZE];
};//class Array
class item_proxy;
class Array_iterator
: public iterator_facade
<
Array_iterator,
int, // VALUE TYPE
boost::random_access_traversal_tag,
item_proxy // REFERENCE TYPE
>
{
public:
class item_proxy {
public:
item_proxy(const Array_iterator &it):
m_rIterator(it) {}
item_proxy& operator=(int i) {
m_rIterator.m_pArray->
Set(m_rIterator.m_index,
i);
return *this;
}
item_proxy& operator=(item_proxy const& rhs) {
operator=((int)rhs);
return *this;
}
operator int() const {
return
m_rIterator.m_pArray->
Get(m_rIterator.m_index);
}
private:
Array_iterator const &m_rIterator;
};//class item_proxy
public:
Array_iterator():m_pArray(0) {}
Array_iterator(Array& array, int index = 0):
m_pArray(&array), m_index(0) {}
private:
friend class boost::iterator_core_access;
void increment() { ++m_index; }
void decrement() { --m_index; }
void advance(int n) { m_index += n; }
int distance_to(Array_iterator const& rhs) {
if(m_pArray != rhs.m_pArray) { return -1; }
return rhs.m_index - m_index;
}
bool equal(Array_iterator const& rhs) const {
return m_pArray == rhs.m_pArray &&
m_index == rhs.m_index;
}
item_proxy dereference() const {
return item_proxy(*this);
}
Array *m_pArray;
int m_index;
};//class Array_iterator
Array_iterator array_begin(Array& array) {
return Array_iterator(array);
}
Array_iterator array_end(Array& array) {
return Array_iterator(array, ARRAY_SIZE);
}
int value_generator() {
static int i = 0;
return ++i;
}
int _tmain(int argc, _TCHAR* argv[])
{
Array a;
generate(array_begin(a), array_end(a), value_generator);
// ERROR!
copy(array_begin(a), array_end(a),
ostream_iterator<int>(cout, " "));
return 0;
}
------------------------------------------------------------------------
David Abrahams
gusz1ļ¼ freemail.hu