Boost.RangeEx merged into Boost.Range

[SVN r60897]

doc/reference/adaptors/map_keys.qbk

@@ -0,0 +1,47 @@
+[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:] `SinglePassRange`
+
+[section:map_keys_example map_keys example]
+``
+#include <boost/range/adaptor/map.hpp>
+#include <boost/range/algorithm/copy.hpp>
+#include <boost/assign.hpp>
+#include <algorithm>
+#include <iostream>
+#include <map>
+#include <vector>
+
+int main(int argc, const char* argv[])
+{
+    using namespace boost::assign;
+    using namespace boost::adaptors;
+
+    std::map<int,int> input;
+    for (int i = 0; i < 10; ++i)
+        input.insert(std::make_pair(i, i * 10));
+
+    boost::copy(
+        input | map_keys,
+        std::ostream_iterator<int>(std::cout, ","));
+
+    return 0;
+}
+``
+[endsect]
+
+This would produce the output:
+``
+0,1,2,3,4,5,6,7,8,9
+``
+[endsect]
+
+