[PATCH] Python-like join function for string lists

[Joerg Sonnenberger]

This adds a function to join a list/vector/whatever of strings or StringRefs. For forward iterators, an optimised two pass version is used that computes the result size first.

http://llvm-reviews.chandlerc.com/D1585

Files:
  unittests/ADT/StringRefTest.cpp
  include/llvm/ADT/StringExtras.h

Index: unittests/ADT/StringRefTest.cpp
===================================================================
--- unittests/ADT/StringRefTest.cpp
+++ 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 @@
   }
 }
 
+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;
+  ASSERT_TRUE(v1_join1);
+  bool v1_join2 = join(v1.begin(), v1.end(), ":") == join_result2;
+  ASSERT_TRUE(v1_join2);
+  bool v1_join3 = join(v1.begin(), v1.end(), "::") == join_result3;
+  ASSERT_TRUE(v1_join3);
+
+  bool v2_join1 = join(v2.begin(), v2.begin() + 1, ":") == join_result1;
+  ASSERT_TRUE(v2_join1);
+  bool v2_join2 = join(v2.begin(), v2.end(), ":") == join_result2;
+  ASSERT_TRUE(v2_join2);
+  bool v2_join3 = join(v2.begin(), v2.end(), "::") == join_result3;
+  ASSERT_TRUE(v2_join3);
+}
+
 } // end anonymous namespace
Index: include/llvm/ADT/StringExtras.h
===================================================================
--- include/llvm/ADT/StringExtras.h
+++ 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 +160,52 @@
   }
 }
 
+template <typename iter>
+static inline std::string join_impl(iter Begin, iter 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 iter>
+static inline std::string join_impl(iter Begin, iter End, StringRef Separator,
+  std::forward_iterator_tag)
+{
+  std::string S;
+  if (Begin == End)
+    return S;
+
+  size_t Len = 0;
+  for (iter I = Begin; I != End; ++I)
+    Len += (*Begin).size() + Separator.size();
+  Len -= Separator.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 iter>
+static inline std::string join(iter Begin, iter End, StringRef Separator)
+{
+  typedef typename std::iterator_traits<iter>::iterator_category tag;
+  return join_impl(Begin, End, Separator, tag());
+}
+
 } // End llvm namespace
 
 #endif
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