On Tue, 25 Apr 2006 23:11:26 -0300, Greg Link wrote:
I would agree with you there - a 'foreach' would do what I need as
well, but as I'm not 100% familiar with the way libraries such as
boost are implemented, I worry that making your own control structure
is much more difficult than making an accessor/modifier pair. I can't
even imagine the syntax needed to convert the following into a
theoretical boost-defined 'foreach'
I didn't mean new sintax, but a std::for_each work-alike.
double previous = 0;
double accumulator = 0;
for(iterator_t myIterator = m_array.data(); myIterator != m_array.end
(); myIterator++)
{
accumulator += (*myIterator);
(*myIterator) *= previous
accumulator = (previous > 7) ? (do_function(accumulator)) : (0);
}
You can do that with Boost.Lambda:
#include
#include
#include
#include <algorithm>
int main()
{
double previous = 0;
double accumulator = 0;
double d[3] = {1, 2, 3};
using boost::lambda::_1;
using boost::lambda::if_then_else_return;
using boost::lambda::var;
using boost::lambda::bind;
std::for_each(&d[0], &d[3], (
accumulator += _1,
_1 *= previous,
var(accumulator) =
if_then_else_return(var(previous) > 7,
bind(&do_function, accumulator),
0)));
}
I spend some time today writing a std::for_each-like function for
multiarrays. This works correctly for subviews, but isn't as convenient
as an iterator. You can't iterate through two multiarrays at the same
time, for example. I only tested with MSVC8, so there may be some
typenames missing. Here it is:
template
struct for_each_impl
{
F f;
for_each_impl(F f) : f(f) {}
void operator()(MA& ma)
{
std::for_each(ma.begin(), ma.end(), for_each_impl(f));
}
};
template
struct for_each_impl
{
F f;
for_each_impl(F f) : f(f) {}
void operator()(Ref r)
{
f(r);
}
};
template
void for_each(MA& ma, F f)
{
for_each_impl impl(f);
impl(ma);
}
And a test:
typedef boost::multi_array array_type;
typedef array_type::index index;
array_type myarray(boost::extents[3][4][2]);
typedef array_type::index_range range;
array_type::array_view<3>::type myview =
myarray[ boost::indices[range(0,2)][range(1,3)][range(0,4,2)] ];
for_each(myview, _1 = 56);
Hope that helps.
Bruno
