1[/ 2 Copyright 2010 Neil Groves 3 Distributed under the Boost Software License, Version 1.0. 4 (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 5/] 6[section:map_keys map_keys] 7 8[table 9 [[Syntax] [Code]] 10 [[Pipe] [`rng | boost::adaptors::map_keys`]] 11 [[Function] [`boost::adaptors::keys(rng)`]] 12] 13 14* [*Precondition:] The `value_type` of the range is an instantiation of `std::pair`. 15* [*Postcondition:] For all elements `x` in the returned range, `x` is the result of `y.first` where `y` is the corresponding element in the original range. 16* [*Range Category:] __single_pass_range__ 17* [*Range Return Type:] `boost::select_first_range<decltype(rng)>` 18* [*Returned Range Category:] The range category of `rng`. 19 20[section:map_keys_example map_keys example] 21[import ../../../test/adaptor_test/map_keys_example.cpp] 22[map_keys_example] 23[endsect] 24 25This would produce the output: 26`` 270,1,2,3,4,5,6,7,8,9, 28`` 29[endsect] 30 31 32