copy_n: return canonical iterator instead of pair (#4633)

groups/bsl/bsl+bslhdrs/bsl_algorithm.h

@@ -23,10 +23,6 @@ BSLS_IDENT("$Id: $")
 
 #include <bslstl_algorithm.h>
 
-#ifndef BDE_OPENSOURCE_PUBLICATION // STP
-#include <bslstp_exalgorithm.h>
-#endif  // BDE_OPENSOURCE_PUBLICATION -- STP
-
 #endif
 
 // ----------------------------------------------------------------------------

groups/bsl/bslim/bslim_bslstandardheadertest.t.cpp

@@ -972,17 +972,12 @@ int main(int argc, char *argv[])
             out.push_back(i + 10);
         }
 
-        ConstIterator EXPECTED_IN  = in.cbegin() + NUM_ITEMS_TO_COPY;
-        Iterator      EXPECTED_OUT = out.begin() + NUM_ITEMS_TO_COPY;
+        ConstIterator EXPECTED_OUT = out.begin() + NUM_ITEMS_TO_COPY;
 
-        bsl::pair<ConstIterator, Iterator> result =
+        Iterator result =
                       bsl::copy_n(in.cbegin(), NUM_ITEMS_TO_COPY, out.begin());
 
-        ConstIterator resultIn  = result.first;
-        Iterator      resultOut = result.second;
-
-        ASSERT(EXPECTED_IN  == resultIn);
-        ASSERT(EXPECTED_OUT == resultOut);
+        ASSERT(EXPECTED_OUT == result);
 
         for (size_t i = 0; i < NUM_ITEMS_TO_COPY; ++i) {
             ASSERTV(in[i], out[i], in[i] == out[i]);

groups/bsl/bslstl/bslstl_algorithm.h

@@ -170,11 +170,8 @@ namespace bsl {
     using std::any_of;
     using std::copy_if;
 
-    // 'copy_n' is implemented separately in 'bslstp_exalgorithm' for backwards
-    // compatibility with the previous STLport definition (which differs from
-    // the platform implementation).
-    //
-    // using std::(copy_n);
+    using std::copy_n;
+    #define BSLSTL_ALGORITHM_COPY_N_IS_ALIASED
 
     using std::find_if_not;
     using std::is_heap;
@@ -487,6 +484,21 @@ namespace ranges {
 
 }  // close namespace bsl
 
+
+
+#ifndef BSLSTL_ALGORITHM_COPY_N_IS_ALIASED
+namespace bsl {
+template <class t_INPUT_ITERATOR, class t_SIZE, class t_OUTPUT_ITERATOR>
+inline
+t_OUTPUT_ITERATOR copy_n(t_INPUT_ITERATOR  first,
+                         t_SIZE            count,
+                         t_OUTPUT_ITERATOR result);
+    // Copy the specified 'count' elements from the specified 'first' to the
+    // specified 'result'.  Return an iterator pointing past the last copied
+    // element in the output range.
+}  // close namespace bsl
+#endif  // BSLSTL_ALGORITHM_COPY_N_IS_ALIASED
+
 // ============================================================================
 //                            INLINE DEFINITIONS
 // ============================================================================
@@ -672,6 +684,18 @@ bsl::search(FORWARD_ITERATOR first,
 }
 #endif  // BSLS_LIBRARYFEATURES_HAS_CPP17_SEARCH_OVERLOAD
 
+#ifndef BSLSTL_ALGORITHM_COPY_N_IS_ALIASED
+template <class t_INPUT_ITERATOR, class t_SIZE, class t_OUTPUT_ITERATOR>
+inline
+t_OUTPUT_ITERATOR bsl::copy_n(t_INPUT_ITERATOR  first,
+                              t_SIZE            count,
+                              t_OUTPUT_ITERATOR result)
+{
+    return BloombergLP::bslstl::AlgorithmUtil::copyN(first,
+                                                     count,
+                                                     result);
+}
+#endif  // BSLSTL_ALGORITHM_COPY_N_IS_ALIASED
 
 #endif  // INCLUDED_BSLSTL_ALGORITHM