Add overload of join_string() that takes a function argument

src/util/string_utils.h

@@ -47,26 +47,51 @@ std::string trim_from_last_delimiter(
 /// \param b: Iterator pointing to first item to print
 /// \param e: Iterator pointing past last item to print
 /// \param delimiter: Object to print between each item in the iterator range
+/// \param transform_func: Transform to apply to the value returned by the
+///   iterator
 /// \return A reference to the ostream that was passed in
-template<typename Stream, typename It, typename Delimiter>
+template <
+  typename Stream,
+  typename It,
+  typename Delimiter,
+  typename TransformFunc>
 Stream &join_strings(
-  Stream &os,
+  Stream &&os,
   const It b,
   const It e,
-  const Delimiter &delimiter)
+  const Delimiter &delimiter,
+  TransformFunc &&transform_func)
 {
   if(b==e)
   {
     return os;
   }
-  os << *b;
+  os << transform_func(*b);
   for(auto it=std::next(b); it!=e; ++it)
   {
-    os << delimiter << *it;
+    os << delimiter << transform_func(*it);
   }
   return os;
 }
 
+/// Prints items to an stream, separated by a constant delimiter
+/// \tparam It: An iterator type
+/// \tparam Delimiter: A delimiter type which supports printing to ostreams
+/// \param os: An ostream to write to
+/// \param b: Iterator pointing to first item to print
+/// \param e: Iterator pointing past last item to print
+/// \param delimiter: Object to print between each item in the iterator range
+/// \return A reference to the ostream that was passed in
+template <typename Stream, typename It, typename Delimiter>
+Stream &
+join_strings(Stream &&os, const It b, const It e, const Delimiter &delimiter)
+{
+  using value_type = decltype(*b);
+  // Call auxiliary function with identity function
+  return join_strings(
+    os, b, e, delimiter, [](const value_type &x) { return x; });
+}
+
 /// Generic escaping of strings; this is not meant to be a particular
 /// programming language.
 std::string escape(const std::string &);

unit/Makefile

@@ -69,7 +69,8 @@ SRC += analyses/ai/ai.cpp \
        util/simplify_expr.cpp \
        util/small_map.cpp \
        util/small_shared_two_way_ptr.cpp \
-       util/std_expr.cpp \
+	util/std_expr.cpp \
+       util/string_utils/join_string.cpp \
        util/string_utils/split_string.cpp \
        util/string_utils/strip_string.cpp \
        util/symbol_table.cpp \

unit/util/string_utils/join_string.cpp

@@ -0,0 +1,44 @@
+/*******************************************************************\
+
+Module: Unit tests of join_string
+
+Author: Diffblue Ltd.
+
+\*******************************************************************/
+
+/// \file
+/// join_string Unit Tests
+
+#include <sstream>
+#include <string>
+#include <vector>
+
+#include <testing-utils/use_catch.h>
+#include <util/string_utils.h>
+
+TEST_CASE(
+  "join_strings() should apply the function argument its passed to the "
+  "elements of the container",
+  "[core][utils][string_utils][join_strings]")
+{
+  std::vector<int> vec{1, 2, 3};
+  auto result = join_strings(
+                  std::ostringstream(),
+                  vec.begin(),
+                  vec.end(),
+                  "-",
+                  [](int x) { return std::to_string(x + 1); })
+                  .str();
+  REQUIRE(result == "2-3-4");
+}
+
+TEST_CASE(
+  "join_strings() when passed no function argument should apply the default "
+  "identity function to the elements of the container",
+  "[core][utils][string_utils][join_strings]")
+{
+  std::vector<int> vec{1, 2, 3};
+  auto result =
+    join_strings(std::ostringstream(), vec.begin(), vec.end(), ",").str();
+  REQUIRE(result == "1,2,3");
+}