[/
    Copyright 2010 Neil Groves
    Distributed under the Boost Software License, Version 1.0.
    (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
/]
[section:map_keys map_keys]

[table
    [[Syntax] [Code]]
    [[Pipe] [`rng | boost::adaptors::map_keys`]]
    [[Function] [`boost::adaptors::keys(rng)`]]
]

* [*Precondition:] The `value_type` of the range is an instantiation of `std::pair`.
* [*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.
* [*Range Category:] __single_pass_range__
* [*Range Return Type:] `boost::select_first_range<decltype(rng)>`
* [*Returned Range Category:] The range category of `rng`.

[section:map_keys_example map_keys example]
[import ../../../test/adaptor_test/map_keys_example.cpp]
[map_keys_example]
[endsect]

This would produce the output:
``
0,1,2,3,4,5,6,7,8,9,
``
[endsect]