On 09/01/2016 05:48 PM, Remko Tronçon wrote:

Hi,

I have the following piece of code:

std::vectorstd::string list1; std::vectorstd::string list2; push_back(list2, list1 | transformed([](const auto& w) { return w; }) | sliced(0, 1));

This compiles fine with CLang, but with GCC I get the error:

/usr/include/boost/optional/optional.hpp:546:64: error: use of deleted function 'main(int, const char**)::& main(int, const char**)::::operator=(const main(int, const char**)::&)' void assign_value ( rval_reference_type val ) { get_impl() = static_cast(val); }

~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.cpp:46:19: note: a lambda closure type has a deleted copy assignment operator | transformed([](const auto& w) { return w; })

When I replace the lambda by a regular function, the code compiles; when I don't use 'sliced' (but pipe it to e.g. 'transformed' instead), the code also compiles.

Is there a way to make this code compile with a lambda?

You can work around that using the unary plus in order to explicitely trigger the implicit convertion from your capture-less lambda to a function pointer. list1 | transformed(+[](const std::string& w) { return w; }) | sliced(0, 1); This is a workaround, though. I still think your original problem is an issue in the Boost.Range library and should be properly fixed there.

thanks! Remko

PS: I'm using GCC 6.2.0 with Boost 1.61.

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