cmStringAlgorithms: Add faster cmJoin overloads for strings

cmJoin() is often used with std::string ranges. Generic implementation
uses std::ostringstream which is not optimal. With strings we can avoid
operator<<() and make much faster implementation. Additional 'initial'
argument is useful for cmStringCommand.cxx:HandleAppendCommand().

1 files changed, 50 insertions, 0 deletions

diff --git a/Source/cmStringAlgorithms.cxx b/Source/cmStringAlgorithms.cxx
index 71d28a4..e0af281 100644
--- a/Source/cmStringAlgorithms.cxx
+++ b/Source/cmStringAlgorithms.cxx
@@ -7,6 +7,7 @@
 #include <cstddef> // IWYU pragma: keep
 #include <cstdio>
 #include <cstdlib>
+#include <iterator>
 
 std::string cmTrimWhitespace(cm::string_view str)
 {
@@ -323,3 +324,52 @@ bool cmStrToULong(std::string const& str, unsigned long* value)
 {
   return cmStrToULong(str.c_str(), value);
 }
+
+template <typename Range>
+std::size_t getJoinedLength(Range const& rng, cm::string_view separator)
+{
+  std::size_t rangeLength{};
+  for (auto const& item : rng) {
+    rangeLength += item.size();
+  }
+
+  auto const separatorsLength = (rng.size() - 1) * separator.size();
+
+  return rangeLength + separatorsLength;
+}
+
+template <typename Range>
+std::string cmJoinImpl(Range const& rng, cm::string_view separator,
+                       cm::string_view initial)
+{
+  if (rng.empty()) {
+    return { std::begin(initial), std::end(initial) };
+  }
+
+  std::string result;
+  result.reserve(initial.size() + getJoinedLength(rng, separator));
+  result.append(std::begin(initial), std::end(initial));
+
+  auto begin = std::begin(rng);
+  auto end = std::end(rng);
+  result += *begin;
+
+  for (++begin; begin != end; ++begin) {
+    result.append(std::begin(separator), std::end(separator));
+    result += *begin;
+  }
+
+  return result;
+}
+
+std::string cmJoin(std::vector<std::string> const& rng,
+                   cm::string_view separator, cm::string_view initial)
+{
+  return cmJoinImpl(rng, separator, initial);
+}
+
+std::string cmJoin(cmStringRange const& rng, cm::string_view separator,
+                   cm::string_view initial)
+{
+  return cmJoinImpl(rng, separator, initial);
+}