[ADT] Add an version of llvm::join that takes a callable for non-string iterable

[ychen]

• update test

[dblaikie]

Perhaps this should be built by composition with some kind of range transformer (not sure if we have one of those already - maybe we do?), rather than having explicit support in join?

[ychen]

In D85698#2208716, @dblaikie wrote:

Perhaps this should be built by composition with some kind of range transformer (not sure if we have one of those already - maybe we do?), rather than having explicit support in join?

I'm not sure we have anything in-tree to use. I was thinking this as something like std::find_if for std::find. Just for convenience and save a temporary container. To use composition without adding a join overload, we need something like python yield?

[dblaikie]

In D85698#2208785, @ychen wrote:

In D85698#2208716, @dblaikie wrote:

Perhaps this should be built by composition with some kind of range transformer (not sure if we have one of those already - maybe we do?), rather than having explicit support in join?

I'm not sure we have anything in-tree to use. I was thinking this as something like std::find_if for std::find. Just for convenience and save a temporary container. To use composition without adding a join overload, we need something like python yield?

Ah, that's what I was thinking of - join+map_range?

[ychen]

Yeah, that should work. Thanks.

llvm/include/llvm/ADT/StringExtras.h

 
 /// Converts a string from snake-case to camel-case by replacing all occurrences
 /// of '_' followed by a lowercase letter with the letter in uppercase.
 /// Optionally allow capitalization of the first letter (if it is a lowercase
 /// letter)
 std::string convertToCamelFromSnakeCase(StringRef input,
                                         bool capitalizeFirst = false);
 
-namespace detail {
-
-template <typename IteratorT>
-inline std::string join_impl(IteratorT Begin, IteratorT End,
-                             StringRef Separator, std::input_iterator_tag) {
+template <typename IteratorT, typename UnaryFunction>
+inline std::string join(IteratorT Begin, IteratorT End, StringRef Separator,
+                        UnaryFunction F) {
   std::string S;
   if (Begin == End)
     return S;
 
-  S += (*Begin);
+  S += F(*Begin);
   while (++Begin != End) {
     S += Separator;
-    S += (*Begin);
+    S += F(*Begin);
   }
   return S;
 }
 
+/// Joins the strings in the range [R.begin(), R.end()), adding Separator
+/// between the elements.
+template <typename Range, typename UnaryFunction>
+inline std::string join(Range &&R, StringRef Separator, UnaryFunction F) {
+  return join(R.begin(), R.end(), Separator, F);
+}
+
+namespace detail {
+
+template <typename IteratorT>
+inline std::string join_impl(IteratorT Begin, IteratorT End,
+                             StringRef Separator, std::input_iterator_tag) {
+  return join(Begin, End, Separator, [](auto &&S) { return std::forward(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();

llvm/unittests/ADT/StringExtrasTest.cpp

TEST(StringExtrasTest, Join) {
   EXPECT_EQ("foo", join(Items.begin(), Items.end(), " <sep> "));
 
   Items = {"foo", "bar"};
   EXPECT_EQ("foo <sep> bar", join(Items.begin(), Items.end(), " <sep> "));
 
   Items = {"foo", "bar", "baz"};
   EXPECT_EQ("foo <sep> bar <sep> baz",
             join(Items.begin(), Items.end(), " <sep> "));
+
+  std::vector<unsigned> Integers = {1, 2, 3};
+  EXPECT_EQ("1 <sep> 2 <sep> 3",
+            join(Integers.begin(), Integers.end(), " <sep> ",
+                 [](auto I) { return StringRef(utostr(I)); }));
+
+  Integers = {4, 5, 6};
+  EXPECT_EQ("4 <sep> 5 <sep> 6",
+            join(Integers, " <sep> ", [](auto I) { return utostr(I); }));
+  EXPECT_EQ("4 <sep> 5 <sep> 6", join(std::move(Integers), " <sep> ",
+                                      [](auto I) { return utostr(I); }));
 }
 
 TEST(StringExtrasTest, JoinItems) {
   const char *Foo = "foo";
   std::string Bar = "bar";
   llvm::StringRef Baz = "baz";
   char X = 'x';