From f57a80f4942dafdb56e854d42af83abaf949ff9d Mon Sep 17 00:00:00 2001
From: Joerg Sonnenberger <joerg@bec.de>
Date: Tue, 3 Sep 2013 20:43:54 +0000
Subject: [PATCH] Add a Python-like join function to merge a list of strings
 with a separator between each two elements.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189846 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/StringExtras.h | 43 +++++++++++++++++++++++++++++++++
 unittests/ADT/StringRefTest.cpp | 27 +++++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/include/llvm/ADT/StringExtras.h b/include/llvm/ADT/StringExtras.h
index d2887c5c2c5..56dbb5b8068 100644
--- a/include/llvm/ADT/StringExtras.h
+++ b/include/llvm/ADT/StringExtras.h
@@ -14,6 +14,7 @@
 #ifndef LLVM_ADT_STRINGEXTRAS_H
 #define LLVM_ADT_STRINGEXTRAS_H
 
+#include <iterator>
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DataTypes.h"
 
@@ -159,6 +160,48 @@ static inline StringRef getOrdinalSuffix(unsigned Val) {
   }
 }
 
+template <typename IteratorT>
+inline std::string join_impl(IteratorT Begin, IteratorT End,
+                             StringRef Separator, std::input_iterator_tag) {
+  std::string S;
+  if (Begin == End)
+    return S;
+
+  S += (*Begin);
+  while (++Begin != End) {
+    S += Separator;
+    S += (*Begin);
+  }
+  return S;
+}
+
+template <typename IteratorT>
+inline std::string join_impl(IteratorT Begin, IteratorT End,
+                             StringRef Separator, std::forward_iterator_tag) {
+  std::string S;
+  if (Begin == End)
+    return S;
+
+  size_t Len = (std::distance(Begin, End) - 1) * Separator.size();
+  for (IteratorT I = Begin; I != End; ++I)
+    Len += (*Begin).size();
+  S.reserve(Len);
+  S += (*Begin);
+  while (++Begin != End) {
+    S += Separator;
+    S += (*Begin);
+  }
+  return S;
+}
+
+/// Joins the strings in the range [Begin, End), adding Separator between
+/// the elements.
+template <typename IteratorT>
+inline std::string join(IteratorT Begin, IteratorT End, StringRef Separator) {
+  typedef typename std::iterator_traits<IteratorT>::iterator_category tag;
+  return join_impl(Begin, End, Separator, tag());
+}
+
 } // End llvm namespace
 
 #endif
diff --git a/unittests/ADT/StringRefTest.cpp b/unittests/ADT/StringRefTest.cpp
index fa87cd0e2c8..3cb6143a42b 100644
--- a/unittests/ADT/StringRefTest.cpp
+++ b/unittests/ADT/StringRefTest.cpp
@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/raw_ostream.h"
@@ -477,6 +478,32 @@ TEST(StringRefTest, getAsUnsignedIntegerBadStrings) {
   }
 }
 
+static const char *join_input[] = { "a", "b", "c" };
+static const char join_result1[] = "a";
+static const char join_result2[] = "a:b:c";
+static const char join_result3[] = "a::b::c";
 
+TEST(StringRefTest, joinStrings) {
+  std::vector<StringRef> v1;
+  std::vector<std::string> v2;
+  for (size_t i = 0; i < array_lengthof(join_input); ++i) {
+    v1.push_back(join_input[i]);
+    v2.push_back(join_input[i]);
+  }
+
+  bool v1_join1 = join(v1.begin(), v1.begin() + 1, ":") == join_result1;
+  EXPECT_TRUE(v1_join1);
+  bool v1_join2 = join(v1.begin(), v1.end(), ":") == join_result2;
+  EXPECT_TRUE(v1_join2);
+  bool v1_join3 = join(v1.begin(), v1.end(), "::") == join_result3;
+  EXPECT_TRUE(v1_join3);
+
+  bool v2_join1 = join(v2.begin(), v2.begin() + 1, ":") == join_result1;
+  EXPECT_TRUE(v2_join1);
+  bool v2_join2 = join(v2.begin(), v2.end(), ":") == join_result2;
+  EXPECT_TRUE(v2_join2);
+  bool v2_join3 = join(v2.begin(), v2.end(), "::") == join_result3;
+  EXPECT_TRUE(v2_join3);
+}
 
 } // end anonymous namespace