[iterator] transform_iterator should use boost::result_of to determine functor result type

[anonymous]

transform_iterator should use boost::result_of to determine result type of functor instead of nested result_type.

[debionne@…]

transform_iterator.hpp patch for boost 1.39

[debionne@…]

transform_iterator_test.cpp patch for boost 1.39

[debionne@…]

The patchs above changes the mechanism that computes the default result type of the given UnaryFunction to use boost::result_of. Consequently, transform_iterator now support polymorphic object function (i.e. function wich result type depends on the arguments type). Such a function object must implement the result_of 'protocol', that is implement a nested result structure such as :

template <class FArgs> struct result; template <class F, class T> struct result<F(T)> {typedef whatever<T>::type type};

A polymorphic object function is added to the tests.

[Jeremiah Willcock]

(In [62625]) Applied patches from #1427; fixes #1427

[mimomorin@…]

Reopened, until merged to release.

[Marshall Clow]

(In [67792]) Merging fixes to release; fixes #2294 fixes #4918 fixes #3645 refs #2823 refs #1427 refs #2893

[mimomorin@…]

r67792 does not seem to do anything with transform_iterator.hpp. Is there something missing?

[Marshall Clow]

(In [68076]) Merging fixes to release; Fixes #1427

[mimomorin@…]

I've experimented with the updated transform_iterator, and found a discrepancy between code and document.

The document says that the (default) reference member of transform_iterator is

result_of<UnaryFunction(iterator_traits<Iterator>::reference)>::type

But the code uses

result_of<UnaryFunction(iterator_traits<Iterator>::value_type)>::type

We should modify the code to use reference instead of value_type, because

• the discrepancy is confusing for users
• reference better interacts with the result_of protocol than value_type

The current code in trunk/release causes compiler error in the following code:

#include <boost/array.hpp>
#include <boost/iterator/transform_iterator.hpp>
#include <boost/spirit/include/phoenix.hpp>

int main(int argc, char* argv[])
{
    boost::array<int, 3> ar = {{}};
    
    *boost::make_transform_iterator(ar.cbegin(), boost::phoenix::arg_names::_1);
    
    return 0;
}

I will attach a patch for fixing this.

Sorry for reopening this ticket repeatedly.

[mimomorin@…]

A patch against trunk (boost/iterator/transform_iterator.hpp)

[mimomorin@…]

A patch against trunk (libs/iterator/test/transform_iterator_test.cpp)

[Marshall Clow]

I've committed these patches as [68205]

[Daniel James]

(In [68524]) Revert [68076], refs #1427.

Will try to fix this properly in 1.47.

[Daniel James]

(In [70715]) Iterator: Use boost::result_of to determine nested result type of function in transform_iterator. Fixes #1427.