On Fri, Jul 31, 2015 at 8:14 AM, Nat Goodspeed wrote:

On Thu, Jul 30, 2015 at 5:08 PM, Edward Diener wrote:

...

Can you not use the function_output_iterator to accomplish what you want to do ?

Please point me to it? I can't seem to find any such thing in Boost 1.58.

Never mind. Silly me. I was looking under the iterator library.

On 7/31/15 8:40 AM, dariomt wrote:

Edward Diener writes:

...

On 7/30/2015 7:06 AM, dariomt <at> gmail.com wrote:

...

Here is my problem: for any given algorithm that writes its output

into

...

...

an output iterator, I'd like to apply a transformation *before* writing to the output iterator.

e.g. inside the algorithm the output iterator is dereferenced and incremented to write each result, typically like this:

*output++ = ith_result;

I'd like to wrap the output iterator with a unary function func such that the effect is equivalent to:

*output++ = func( ith_result );

I'm looking at the adaptors in Boost.Iterator but I cannot find a suitable one.

Am I missing anything? Is there a better approach?

Can you not use the function_output_iterator to accomplish what you want to do ?

IIUC the function_output_iterator "fakes" an output iterator with a function object that gets called for each element written to the iterator.

I need to wrap *both* an actual output iterator and a function object, and I need to apply the function *before* writing to the actual output iterator.

Given that the output iterator is written by dereference and assignment, I think I would need some kind of proxy reference, that when assigned to applies the function before doing the actual assignment.

That looks ugly, so I'm asking here for a more elegant solution :)

how is what you want to do different from: boost::copy( myrange | transformed(func), outputitr ); Jeff

The only way I could see this different from Jeff proposal is if somehow yous functor to transform the result is dependant on the traversal of the sequence or the order of the element. Other I don't see why you couldn't do my_algo(input_range | trasnformed(func), out). Cheers, Stephane On Mon, Aug 3, 2015 at 12:03 PM dariomt wrote:

Jeff Flinn writes:

...

On 7/31/15 8:40 AM, dariomt wrote:

...

Edward Diener writes:

...

On 7/30/2015 7:06 AM, dariomt <at> gmail.com wrote:

...

Here is my problem: for any given algorithm that writes its output

into

...

...

an output iterator, I'd like to apply a transformation *before* writing to the output iterator.

e.g. inside the algorithm the output iterator is dereferenced and incremented to write each result, typically like this:

*output++ = ith_result;

I'd like to wrap the output iterator with a unary function func

such

...

...

...

...

that the effect is equivalent to:

*output++ = func( ith_result );

I'm looking at the adaptors in Boost.Iterator but I cannot find a suitable one.

Am I missing anything? Is there a better approach?

Can you not use the function_output_iterator to accomplish what you want to do ?

IIUC the function_output_iterator "fakes" an output iterator with a function object that gets called for each element written to the iterator.

I need to wrap *both* an actual output iterator and a function object, and I need to apply the function *before* writing to the actual output iterator.

Given that the output iterator is written by dereference and assignment, I think I would need some kind of proxy reference, that when assigned to applies the function before doing the actual assignment.

That looks ugly, so I'm asking here for a more elegant solution :)

how is what you want to do different from:

boost::copy( myrange | transformed(func), outputitr );

Jeff

What if myrange is the output of an algorithm, but I don't want to copy it into an intermediate range?

e.g. template void my_algo(InputIter first, InputIter last, OutputIter out) { // complex loop traversing input sequence ... // some complicated code to compute each result ... // write each result to output iterator *out++ = ith_result; }

I know I could do it easily in two steps storing the intermediate results.

intermediate_storage tmp; my_algo(input.begin(), input.end(), back_inserter(tmp)); transform(tmp.begin(), tmp.end(), output);

But how to do it in one go, without requiring storage for intermediate results?

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