why std::sort take no template parameter to swap?

[panzhiyong]

Hi there! I wonder why there is no such a overload version of sort
function in STL:

template<class RandomAccessIterator, class Pr, class IterSwap>
void sort(
RandomAccessIterator _First,
RandomAccessIterator _Last,
BinaryPredicate _Comp,
IterSwap _Swap
);

It seems that std::sort works only with "simple" element, which has
default constructor and value semantics. So the problem rises when I
want to sort a collection of point coordinates, like:

// sort 2D points, note that I use double(*)[2] to hold points'
coordinates.
void SortPoint(double coords[][2], int n)
{
sort(coords, coords + n, PointLess()); // compile error in
std::swap, require l-value.
}

What I want is somthing like:

void SortPoint(double coords[][2], int n)
{
sort(coords, coords + n, PointLess(), PointSwap());
}

Wish somebody to share his(her) thought about this!

// compare points
class PointLess
{
public:
bool operator() (double* a, double* b)
{
if(abs(a[0] - b[0]) tolerance)
return a[0] < b[0];

return a[1] < b[1];
}
};

// swap points
class PointSwap
{
public:
void operator() (double* a, double* b)
{
swap(a[0], b[0]);
swap(a[1], b[1]);
}
};

[Michael DOUBEZ]

panzhiyong a écrit :

Hi there! I wonder why there is no such a overload version of sort
function in STL:

template<class RandomAccessIterator, class Pr, class IterSwap>
void sort(
RandomAccessIterator _First,
RandomAccessIterator _Last,
BinaryPredicate _Comp,
IterSwap _Swap
);

It seems that std::sort works only with "simple" element, which has
default constructor and value semantics. So the problem rises when I
want to sort a collection of point coordinates, like:

// sort 2D points, note that I use double(*)[2] to hold points'
coordinates.
void SortPoint(double coords[][2], int n)
{
sort(coords, coords + n, PointLess()); // compile error in
std::swap, require l-value.
}

What I want is somthing like:

void SortPoint(double coords[][2], int n)
{
sort(coords, coords + n, PointLess(), PointSwap());
}

Wish somebody to share his(her) thought about this!

// compare points
class PointLess
{
public:
bool operator() (double* a, double* b)
{
if(abs(a[0] - b[0]) tolerance)
return a[0] < b[0];

return a[1] < b[1];
}
};

// swap points
class PointSwap
{
public:
void operator() (double* a, double* b)
{
swap(a[0], b[0]);
swap(a[1], b[1]);
}
};

You could use an iterator_facade.Boost provides an implmentation but it
is included in TR1 so it is next to standard.

You basically wrap a double* pointer but:
* iterator increments are done by twos
* distance is given divided by two
* return type is a struct { double& x; double& y;}; to allow copy

Seems a bit of a pain but you only need to implement it once. I have
very little experience about it so I cannot evaluate if it is worth the
trouble.

Here is the example from Boost:
http://boost.org/libs/iterator/doc/i...torial-example
Michael